NETCONF Working Group K. Watsen
Internet-Draft Watsen Networks
Intended status: Standards Track April 7, 2019
Expires: October 9, 2019

NETCONF Client and Server Models
draft-ietf-netconf-netconf-client-server-11

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:

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

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

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

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 https://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on October 9, 2019.

Copyright Notice

Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved.

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


Table of Contents

1. Introduction

This document defines two YANG [RFC7950] modules, one module to configure a NETCONF [RFC6241] client and the other module to configure a NETCONF server. Both modules support both NETCONF over SSH [RFC6242] and NETCONF over TLS [RFC7589] and NETCONF Call Home connections [RFC8071].

2. 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.

3. 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, using either the SSH and TLS transport protocols.

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

3.1. Tree Diagram

The following tree diagram [RFC8340] provides an overview of the data model for the "ietf-netconf-client" module.

This tree diagram only shows the nodes defined in this module; it does show the nodes defined by "grouping" statements used by this module.

Please see Appendix A.1 for a tree diagram that illustrates what the module looks like with all the "grouping" statements expanded.

module: ietf-netconf-client
  +--rw netconf-client
     +---u netconf-client-grouping

  grouping netconf-client-grouping
    +-- initiate! {initiate}?
    |  +-- netconf-server* [name]
    |     +-- name?                 string
    |     +-- endpoints
    |     |  +-- endpoint* [name]
    |     |     +-- name?        string
    |     |     +-- (transport)
    |     |        +--:(ssh) {ssh-initiate}?
    |     |        |  +-- ssh
    |     |        |     +---u netconf-client-grouping
    |     |        +--:(tls) {tls-initiate}?
    |     |           +-- tls
    |     |              +---u netconf-client-grouping
    |     +-- connection-type
    |     |  +-- (connection-type)
    |     |     +--:(persistent-connection)
    |     |     |  +-- persistent!
    |     |     +--:(periodic-connection)
    |     |        +-- periodic!
    |     |           +-- period?         uint16
    |     |           +-- anchor-time?    yang:date-and-time
    |     |           +-- idle-timeout?   uint16
    |     +-- reconnect-strategy
    |        +-- start-with?     enumeration
    |        +-- max-attempts?   uint8
    +-- listen! {listen}?
       +-- idle-timeout?   uint16
       +-- endpoint* [name]
          +-- name?        string
          +-- (transport)
             +--:(ssh) {ssh-listen}?
             |  +-- ssh
             |     +---u netconf-client-grouping
             +--:(tls) {tls-listen}?
                +-- tls
                   +---u netconf-client-grouping

3.2. 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 3.2 of [I-D.ietf-netconf-keystore].

=========== NOTE: '\' line wrapping per BCP XX (RFC XXXX) ===========

<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>
      <endpoints>
        <endpoint>
          <name>corp-fw1.example.com</name>
          <ssh>
            <tcp-client-parameters>
              <remote-address>corp-fw1.example.com</remote-address>
              <keepalives>
                <idle-time>15</idle-time>
                <max-probes>3</max-probes>
                <probe-interval>30</probe-interval>
              </keepalives>
            </tcp-client-parameters>
            <ssh-client-parameters>
              <client-identity>
                <username>foobar</username>
                <public-key>
                  <local-definition>
                    <algorithm xmlns:ct="urn:ietf:params:xml:ns:yang\
:ietf-crypto-types">ct:rsa2048</algorithm>
                    <private-key>base64encodedvalue==</private-key>
                    <public-key>base64encodedvalue==</public-key>
                  </local-definition>
                </public-key>
              </client-identity>
              <server-authentication>
                <pinned-ca-certs>explicitly-trusted-server-ca-certs<\
/pinned-ca-certs>
                <pinned-server-certs>explicitly-trusted-server-certs\
</pinned-server-certs>
              </server-authentication>
              <keepalives>
                <max-wait>30</max-wait>
                <max-attempts>3</max-attempts>
              </keepalives>
            </ssh-client-parameters>
          </ssh>
        </endpoint>
        <endpoint>
          <name>corp-fw2.example.com</name>
          <ssh>
            <tcp-client-parameters>
              <remote-address>corp-fw2.example.com</remote-address>
              <keepalives>
                <idle-time>15</idle-time>
                <max-probes>3</max-probes>
                <probe-interval>30</probe-interval>
              </keepalives>
            </tcp-client-parameters>
            <ssh-client-parameters>
              <client-identity>
                <username>foobar</username>
                <public-key>
                  <local-definition>
                    <algorithm xmlns:ct="urn:ietf:params:xml:ns:yang\
:ietf-crypto-types">ct:rsa2048</algorithm>
                    <private-key>base64encodedvalue==</private-key>
                    <public-key>base64encodedvalue==</public-key>
                  </local-definition>
                </public-key>
              </client-identity>
              <server-authentication>
                <pinned-ca-certs>explicitly-trusted-server-ca-certs<\
/pinned-ca-certs>
                <pinned-server-certs>explicitly-trusted-server-certs\
</pinned-server-certs>
              </server-authentication>
              <keepalives>
                <max-wait>30</max-wait>
                <max-attempts>3</max-attempts>
              </keepalives>
            </ssh-client-parameters>
          </ssh>
        </endpoint>
      </endpoints>
      <connection-type>
        <persistent/>
      </connection-type>
      <reconnect-strategy>
        <start-with>last-connected</start-with>
      </reconnect-strategy>
    </netconf-server>
  </initiate>

  <!-- endpoints to listen for NETCONF Call Home connections on -->
  <listen>
    <endpoint>
      <name>Intranet-facing listener</name>
      <ssh>
        <tcp-server-parameters>
          <local-address>192.0.2.7</local-address>
        </tcp-server-parameters>
        <ssh-client-parameters>
          <client-identity>
            <username>foobar</username>
            <public-key>
              <local-definition>
                <algorithm xmlns:ct="urn:ietf:params:xml:ns:yang:iet\
f-crypto-types">ct:rsa2048</algorithm>
                <private-key>base64encodedvalue==</private-key>
                <public-key>base64encodedvalue==</public-key>
              </local-definition>
            </public-key>
          </client-identity>
          <server-authentication>
            <pinned-ca-certs>explicitly-trusted-server-ca-certs</pin\
ned-ca-certs>
            <pinned-server-certs>explicitly-trusted-server-certs</pi\
nned-server-certs>
            <pinned-ssh-host-keys>explicitly-trusted-ssh-host-keys</\
pinned-ssh-host-keys>
          </server-authentication>
        </ssh-client-parameters>
      </ssh>
    </endpoint>
  </listen>
</netconf-client>

3.3. YANG Module

This YANG module has normative references to [RFC6242], [RFC6991], [RFC7589], [RFC8071], [I-D.kwatsen-netconf-tcp-client-server], [I-D.ietf-netconf-ssh-client-server], and [I-D.ietf-netconf-tls-client-server].

<CODE BEGINS> file "ietf-netconf-client@2019-04-07.yang"
module ietf-netconf-client {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-netconf-client";
  prefix ncc;

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

  import ietf-tcp-client {
    prefix tcpc;
    reference
      "RFC AAAA: YANG Groupings for TCP Clients and TCP Servers";
  }
  import ietf-tcp-server {
    prefix tcps;
    reference
      "RFC AAAA: YANG Groupings for TCP Clients and TCP Servers";
  }

  import ietf-ssh-client {
    prefix sshc;
    revision-date 2019-04-07; // stable grouping definitions
    reference
      "RFC BBBB: YANG Groupings for SSH Clients and SSH Servers";
  }

  import ietf-tls-client {
    prefix tlsc;
    revision-date 2019-04-07; // stable grouping definitions
    reference
      "RFC CCCC: YANG Groupings for TLS Clients and TLS Servers";
  }

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

  contact
    "WG Web:   <http://datatracker.ietf.org/wg/netconf/>
     WG List:  <mailto:netconf@ietf.org>
     Author:   Kent Watsen <mailto:kent+ietf@watsen.net>
     Author:   Gary Wu <mailto:garywu@cisco.com>";

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

     Copyright (c) 2019 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
     (https://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC XXXX
     (https://www.rfc-editor.org/info/rfcXXXX); see the RFC
     itself for full legal notices.;

     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 (RFC 2119)
     (RFC 8174) when, and only when, they appear in all
     capitals, as shown here.";

  revision 2019-04-07 {
    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";
  }

  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";
  }

  // Groupings

  grouping netconf-client-grouping {
    description
      "Top-level grouping for NETCONF client configuration.";
    container initiate {
      if-feature "initiate";
      presence "Enables client to initiate TCP connections";
      description
        "Configures client initiating underlying TCP connections.";
      list netconf-server {
        key "name";
        min-elements 1;
        description
          "List of NETCONF servers the NETCONF client is to
           initiate connections to in parallel.";
        leaf name {
          type string;
          description
            "An arbitrary name for the NETCONF server.";
        }
        container endpoints {
          description
            "Container for the list of endpoints.";
          list endpoint {
            key "name";
            min-elements 1;
            ordered-by user;
            description
              "A user-ordered list of endpoints that the NETCONF
               client will attempt to connect to in the specified
               sequence.  Defining more than one enables
               high-availability.";
            leaf name {
              type string;
              description
                "An arbitrary name for the endpoint.";
            }
            choice transport {
              mandatory true;
              description
                "Selects between available transports.";
              case ssh {
                if-feature "ssh-initiate";
                container ssh {
                  description
                    "Specifies IP and SSH specific configuration
                     for the connection.";
                  uses tcpc:tcp-client-grouping {
                    refine "tcp-client-parameters/remote-port" {
                      default "830";
                      description
                        "The NETCONF client will attempt to connect
                         to the IANA-assigned well-known port value
                         for 'netconf-ssh' (443) if no value is
                         specified.";
                    }
                  }
                  uses sshc:ssh-client-grouping;
                }
              }
              case tls {
                if-feature "tls-initiate";
                container tls {
                  description
                    "Specifies IP and TLS specific configuration
                     for the connection.";
                  uses tcpc:tcp-client-grouping {
                    refine "tcp-client-parameters/remote-port" {
                      default "6513";
                      description
                        "The NETCONF client will attempt to connect
                         to the IANA-assigned well-known port value
                         for 'netconf-tls' (6513) if no value is
                         specified.";
                    }
                  }
                  uses tlsc:tls-client-grouping {
                    refine "tls-client-parameters/client-identity"
                                                  + "/auth-type" {
                      mandatory true;
                      description
                        "NETCONF/TLS clients MUST pass some
                         authentication credentials.";
                    }
                  }
                }
              }
            } // choice transport
          } // list endpoint
        } // container endpoints

        container connection-type {
          description
            "Indicates the NETCONF client's preference for how the
             NETCONF connection is maintained.";
          choice connection-type {
            mandatory true;
            description
              "Selects between available connection types.";
            case persistent-connection {
              container persistent {
                presence "Indicates that a persistent connection is
                          to be maintained.";
                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.";
              }
            }
            case periodic-connection {
              container periodic {
                must 'not (../../endpoints/endpoint/ssh/'
                           + 'tcp-client-parameters/keepalives '
                           + 'or ../../endpoints/endpoint/ssh/'
                           + 'ssh-client-parameters/keepalives '
                           + 'or ../../endpoints/endpoint/tls/'
                           + 'tcp-client-parameters/keepalives '
                           + 'or ../../endpoints/endpoint/tls/'
                           + 'tls-client-parameters/keepalives)';
                presence "Indicates that a periodic connection is
                          to be maintained.";
                description
                  "Periodically connect to the NETCONF server.  The
                   NETCONF server should close the connection upon
                   completing planned activities.

                   This connection type increases resource
                   utilization, albeit with increased delay in
                   NETCONF server to NETCONF client interactions.";
                leaf period {
                  type uint16;
                  units "minutes";
                  default "60";
                  description
                    "Duration of time between periodic connections.";
                }
                leaf anchor-time {
                  type yang:date-and-time {
                    // constrained to minute-level granularity
                    pattern '\d{4}-\d{2}-\d{2}T\d{2}:\d{2}'
                          + '(Z|[\+\-]\d{2}:\d{2})';
                  }
                  description
                    "Designates a timestamp before or after which a
                     series of periodic connections are determined.
                     The periodic connections occur at a whole
                     multiple interval from the anchor time.  For
                     example, for an anchor time is 15 minutes past
                     midnight and a period interval of 24 hours, then
                     a periodic connection will occur 15 minutes past
                     midnight everyday.";
                }
                leaf idle-timeout {
                  type uint16;
                  units "seconds";
                  default 120; // two minutes
                  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 NETCONF client will
                     never drop a session because it is idle.";
                }
              }
            }
          }
        }
        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.";
              }
              enum random-selection {
                description
                  "Indicates that reconnections should start with
                   a random endpoint.";
              }
            }
            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 next endpoint in the list (round robin).";
          }
        }
      } // netconf-server
    } // initiate

    container listen {
      if-feature "listen";
      presence "Enables client to accept call-home connections";
      description
        "Configures client accepting call-home TCP connections.";
      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";
        min-elements 1;
        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.";
              uses tcps:tcp-server-grouping {
                refine "tcp-server-parameters/local-port" {
                  default "4334";
                  description
                    "The NETCONF client will listen on the IANA-
                     assigned well-known port for 'netconf-ch-ssh'
                     (4334) if no value is specified.";
                }
              }
              uses sshc:ssh-client-grouping;
            }
          }
          case tls {
            if-feature "tls-listen";
            container tls {
              description
                "TLS-specific listening configuration for inbound
                 connections.";
              uses tcps:tcp-server-grouping {
                refine "tcp-server-parameters/local-port" {
                  default "4334";
                  description
                    "The NETCONF client will listen on the IANA-
                     assigned well-known port for 'netconf-ch-ssh'
                     (4334) if no value is specified.";
                }
              }
              uses tlsc:tls-client-grouping {
                refine
                  "tls-client-parameters/client-identity/auth-type" {
                  mandatory true;
                  description
                    "NETCONF/TLS clients MUST pass some
                     authentication credentials.";
                }
              }
            }
          }
        } // transport
      } // endpoint
    } // listen
  } // netconf-client

  // Protocol accessible node, for servers that implement this
  // module.

  container netconf-client {
    uses netconf-client-grouping;
    description
      "Top-level container for NETCONF client configuration.";
  }
}
<CODE ENDS>

4. The NETCONF Server Model

The NETCONF server model presented in this section supports both listening for connections as well as initiating call-home connections, using either the SSH and TLS transport protocols.

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

4.1. Tree Diagram

The following tree diagram [RFC8340] provides an overview of the data model for the "ietf-netconf-server" module.

This tree diagram only shows the nodes defined in this module; it does show the nodes defined by "grouping" statements used by this module.

Please see Appendix A.2 for a tree diagram that illustrates what the module looks like with all the "grouping" statements expanded.

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

  grouping netconf-server-grouping
    +-- listen! {listen}?
    |  +-- idle-timeout?   uint16
    |  +-- endpoint* [name]
    |     +-- name?        string
    |     +-- (transport)
    |        +--:(ssh) {ssh-listen}?
    |        |  +-- ssh
    |        |     +---u netconf-server-grouping
    |        +--:(tls) {tls-listen}?
    |           +-- tls
    |              +---u netconf-server-grouping
    +-- call-home! {call-home}?
       +-- netconf-client* [name]
          +-- name?                 string
          +-- endpoints
          |  +-- endpoint* [name]
          |     +-- name?        string
          |     +-- (transport)
          |        +--:(ssh) {ssh-call-home}?
          |        |  +-- ssh
          |        |     +---u netconf-server-grouping
          |        +--:(tls) {tls-call-home}?
          |           +-- tls
          |              +---u netconf-server-grouping
          +-- connection-type
          |  +-- (connection-type)
          |     +--:(persistent-connection)
          |     |  +-- persistent!
          |     +--:(periodic-connection)
          |        +-- periodic!
          |           +-- period?         uint16
          |           +-- anchor-time?    yang:date-and-time
          |           +-- idle-timeout?   uint16
          +-- reconnect-strategy
             +-- start-with?     enumeration
             +-- max-attempts?   uint8

4.2. 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 3.2 of [I-D.ietf-netconf-keystore].

=========== NOTE: '\' line wrapping per BCP XX (RFC XXXX) ===========

<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">

  <!-- endpoints to listen for NETCONF connections on -->
  <listen>
    <endpoint> <!-- listening for SSH connections -->
      <name>netconf/ssh</name>
      <ssh>
        <tcp-server-parameters>
          <local-address>192.0.2.7</local-address>
        </tcp-server-parameters>
        <ssh-server-parameters>
          <server-identity>
            <host-key>
              <name>deployment-specific-certificate</name>
              <public-key>
                <local-definition>
                  <algorithm xmlns:ct="urn:ietf:params:xml:ns:yang:i\
etf-crypto-types">ct:rsa2048</algorithm>
                  <private-key>base64encodedvalue==</private-key>
                  <public-key>base64encodedvalue==</public-key>
                </local-definition>
              </public-key>
            </host-key>
          </server-identity>
          <client-cert-auth>
            <pinned-ca-certs>explicitly-trusted-client-ca-certs</pin\
ned-ca-certs>
            <pinned-client-certs>explicitly-trusted-client-certs</pi\
nned-client-certs>
          </client-cert-auth>
        </ssh-server-parameters>
      </ssh>
    </endpoint>
    <endpoint> <!-- listening for TLS sessions -->
      <name>netconf/tls</name>
      <tls>
        <tcp-server-parameters>
          <local-address>192.0.2.7</local-address>
        </tcp-server-parameters>
        <tls-server-parameters>
          <server-identity>
            <local-definition>
              <algorithm xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-\
crypto-types">ct:rsa2048</algorithm>
              <private-key>base64encodedvalue==</private-key>
              <public-key>base64encodedvalue==</public-key>
              <cert>base64encodedvalue==</cert>
            </local-definition>
          </server-identity>
          <client-authentication>
            <pinned-ca-certs>explicitly-trusted-client-ca-certs</pin\
ned-ca-certs>
            <pinned-client-certs>explicitly-trusted-client-certs</pi\
nned-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-authentication>
        </tls-server-parameters>
      </tls>
    </endpoint>
  </listen>

  <!-- calling home to SSH and TLS based NETCONF clients -->
  <call-home>
    <netconf-client> <!-- SSH-based client -->
      <name>config-mgr</name>
      <endpoints>
        <endpoint>
          <name>east-data-center</name>
          <ssh>
            <tcp-client-parameters>
              <remote-address>east.config-mgr.example.com</remote-ad\
dress>
            </tcp-client-parameters>
            <ssh-server-parameters>
              <server-identity>
                <host-key>
                  <name>deployment-specific-certificate</name>
                  <public-key>
                    <local-definition>
                      <algorithm xmlns:ct="urn:ietf:params:xml:ns:ya\
ng:ietf-crypto-types">ct:rsa2048</algorithm>
                      <private-key>base64encodedvalue==</private-key>
                      <public-key>base64encodedvalue==</public-key>
                    </local-definition>
                  </public-key>
                </host-key>
              </server-identity>
              <client-cert-auth>
                <pinned-ca-certs>explicitly-trusted-client-ca-certs<\
/pinned-ca-certs>
                <pinned-client-certs>explicitly-trusted-client-certs\
</pinned-client-certs>
              </client-cert-auth>
            </ssh-server-parameters>
          </ssh>
        </endpoint>
        <endpoint>
          <name>west-data-center</name>
          <ssh>
            <tcp-client-parameters>
              <remote-address>west.config-mgr.example.com</remote-ad\
dress>
            </tcp-client-parameters>
            <ssh-server-parameters>
              <server-identity>
                <host-key>
                  <name>deployment-specific-certificate</name>
                  <public-key>
                    <local-definition>
                      <algorithm xmlns:ct="urn:ietf:params:xml:ns:ya\
ng:ietf-crypto-types">ct:rsa2048</algorithm>
                      <private-key>base64encodedvalue==</private-key>
                      <public-key>base64encodedvalue==</public-key>
                    </local-definition>
                  </public-key>
                </host-key>
              </server-identity>
              <client-cert-auth>
                <pinned-ca-certs>explicitly-trusted-client-ca-certs<\
/pinned-ca-certs>
                <pinned-client-certs>explicitly-trusted-client-certs\
</pinned-client-certs>
              </client-cert-auth>
            </ssh-server-parameters>
          </ssh>
        </endpoint>
      </endpoints>
      <connection-type>
        <periodic>
          <idle-timeout>300</idle-timeout>
          <period>60</period>
        </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>data-collector</name>
      <endpoints>
        <endpoint>
          <name>east-data-center</name>
          <tls>
            <tcp-client-parameters>
              <remote-address>east.analytics.example.com</remote-add\
ress>
              <keepalives>
                <idle-time>15</idle-time>
                <max-probes>3</max-probes>
                <probe-interval>30</probe-interval>
              </keepalives>
            </tcp-client-parameters>
            <tls-server-parameters>
              <server-identity>
                <local-definition>
                  <algorithm xmlns:ct="urn:ietf:params:xml:ns:yang:i\
etf-crypto-types">ct:rsa2048</algorithm>
                  <private-key>base64encodedvalue==</private-key>
                  <public-key>base64encodedvalue==</public-key>
                  <cert>base64encodedvalue==</cert>
                </local-definition>
              </server-identity>
              <client-authentication>
                <pinned-ca-certs>explicitly-trusted-client-ca-certs<\
/pinned-ca-certs>
                <pinned-client-certs>explicitly-trusted-client-certs\
</pinned-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-authentication>
              <keepalives>
                <max-wait>30</max-wait>
                <max-attempts>3</max-attempts>
              </keepalives>
            </tls-server-parameters>
          </tls>
        </endpoint>
        <endpoint>
          <name>west-data-center</name>
          <tls>
            <tcp-client-parameters>
              <remote-address>west.analytics.example.com</remote-add\
ress>
              <keepalives>
                <idle-time>15</idle-time>
                <max-probes>3</max-probes>
                <probe-interval>30</probe-interval>
              </keepalives>
            </tcp-client-parameters>
            <tls-server-parameters>
              <server-identity>
                <local-definition>
                  <algorithm xmlns:ct="urn:ietf:params:xml:ns:yang:i\
etf-crypto-types">ct:rsa2048</algorithm>
                  <private-key>base64encodedvalue==</private-key>
                  <public-key>base64encodedvalue==</public-key>
                  <cert>base64encodedvalue==</cert>
                </local-definition>
              </server-identity>
              <client-authentication>
                <pinned-ca-certs>explicitly-trusted-client-ca-certs<\
/pinned-ca-certs>
                <pinned-client-certs>explicitly-trusted-client-certs\
</pinned-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-authentication>
              <keepalives>
                <max-wait>30</max-wait>
                <max-attempts>3</max-attempts>
              </keepalives>
            </tls-server-parameters>
          </tls>
        </endpoint>
      </endpoints>
      <connection-type>
        <persistent/>
      </connection-type>
      <reconnect-strategy>
        <start-with>first-listed</start-with>
        <max-attempts>3</max-attempts>
      </reconnect-strategy>
    </netconf-client>
  </call-home>
</netconf-server>

4.3. YANG Module

This YANG module has normative references to [RFC6242], [RFC6991], [RFC7407], [RFC7589], [RFC8071], [I-D.kwatsen-netconf-tcp-client-server], [I-D.ietf-netconf-ssh-client-server], and [I-D.ietf-netconf-tls-client-server].

<CODE BEGINS> file "ietf-netconf-server@2019-04-07.yang"
module ietf-netconf-server {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-netconf-server";
  prefix ncs;

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

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

  import ietf-tcp-client {
    prefix tcpc;
    reference
      "RFC AAAA: YANG Groupings for TCP Clients and TCP Servers";
  }

  import ietf-tcp-server {
    prefix tcps;
    reference
      "RFC AAAA: YANG Groupings for TCP Clients and TCP Servers";
  }

  import ietf-ssh-server {
    prefix sshs;
    revision-date 2019-04-07; // stable grouping definitions
    reference
      "RFC BBBB: YANG Groupings for SSH Clients and SSH Servers";
  }

  import ietf-tls-server {
    prefix tlss;
    revision-date 2019-04-07; // stable grouping definitions
    reference
      "RFC CCCC: YANG Groupings for TLS Clients and TLS Servers";
  }

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

  contact
    "WG Web:   <http://datatracker.ietf.org/wg/netconf/>
     WG List:  <mailto:netconf@ietf.org>
     Author:   Kent Watsen <mailto:kent+ietf@watsen.net>
     Author:   Gary Wu <mailto:garywu@cisco.com>
     Author:   Juergen Schoenwaelder
               <mailto:j.schoenwaelder@jacobs-university.de>";
  description
    "This module contains a collection of YANG definitions
     for configuring NETCONF servers.

     Copyright (c) 2019 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
     (https://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC XXXX
     (https://www.rfc-editor.org/info/rfcXXXX); see the RFC
     itself for full legal notices.;

     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 (RFC 2119)
     (RFC 8174) when, and only when, they appear in all
     capitals, as shown here.";

  revision 2019-04-07 {
    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
      "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";
  }

  // Groupings

  grouping netconf-server-grouping {
    description
      "Top-level grouping for NETCONF server configuration.";
    container listen {
      if-feature "listen";
      presence "Enables server to listen for TCP connections";
      description
        "Configures listen behavior";
      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";
        min-elements 1;
        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.";
              uses tcps:tcp-server-grouping {
                refine "tcp-server-parameters/local-port" {
                  default "830";
                  description
                    "The NETCONF server will listen on the IANA-
                     assigned well-known port value for 'netconf-ssh'
                     (830) if no value is specified.";
                }
              }
              uses sshs:ssh-server-grouping;
            }
          }
          case tls {
            if-feature "tls-listen";
            container tls {
              description
                "TLS-specific listening configuration for inbound
                 connections.";
              uses tcps:tcp-server-grouping {
                refine "tcp-server-parameters/local-port" {
                  default "6513";
                  description
                    "The NETCONF server will listen on the IANA-
                     assigned well-known port value for 'netconf-tls'
                     (6513) if no value is specified.";
                }
              }
              uses tlss:tls-server-grouping {
                refine
                  "tls-server-parameters/client-authentication" {
                  must 'pinned-ca-certs or pinned-client-certs';
                  description
                    "NETCONF/TLS servers MUST validate client
                     certiticates.";
                }
                augment
                  "tls-server-parameters/client-authentication" {
                  description
                    "Augments in the cert-to-name structure.";
                  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";
                  }
                }
              }
            }
          }
        }
      }
    }
    container call-home {
      if-feature "call-home";
      presence "Enables server to initiate TCP connections";
      description "Configures call-home behavior";
      list netconf-client {
        key "name";
        min-elements 1;
        description
          "List of NETCONF clients the NETCONF server is to
           initiate call-home connections to in parallel.";
        leaf name {
          type string;
          description
            "An arbitrary name for the remote NETCONF client.";
        }
        container endpoints {
          description
            "Container for the list of endpoints.";
          list endpoint {
            key "name";
            min-elements 1;
            ordered-by user;
            description
              "A non-empty user-ordered list of endpoints for this
               NETCONF server to try to connect to in sequence.
               Defining more than one enables high-availability.";
            leaf name {
              type string;
              description
                "An arbitrary name for this endpoint.";
            }
            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 tcpc:tcp-client-grouping {
                    refine "tcp-client-parameters/remote-port" {
                      default "4334";
                      description
                        "The NETCONF server will attempt to connect
                         to the IANA-assigned well-known port for
                         'netconf-ch-tls' (4334) if no value is
                         specified.";
                    }
                  }
                  uses sshs:ssh-server-grouping;
                }
              }
              case tls {
                if-feature "tls-call-home";
                container tls {
                  description
                    "Specifies TLS-specific call-home transport
                     configuration.";
                  uses tcpc:tcp-client-grouping {
                    refine "tcp-client-parameters/remote-port" {
                      default "4335";
                      description
                        "The NETCONF server will attempt to connect
                         to the IANA-assigned well-known port for
                         'netconf-ch-tls' (4335) if no value is
                         specified.";
                    }
                  }
                  uses tlss:tls-server-grouping {
                    refine
                      "tls-server-parameters/client-authentication" {
                      must 'pinned-ca-certs or pinned-client-certs';
                      description
                        "NETCONF/TLS servers MUST validate client
                         certiticates.";
                    }
                    augment
                      "tls-server-parameters/client-authentication" {
                      description
                        "Augments in the cert-to-name structure.";
                      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";
                      }
                    }
                  }
                }
              } // tls
            } // choice
          } // endpoint
        } // endpoints
        container connection-type {
          description
            "Indicates the NETCONF server's preference for how the
             NETCONF connection is maintained.";
          choice connection-type {
            mandatory true;
            description
              "Selects between available connection types.";
            case persistent-connection {
              container persistent {
                presence "Indicates that a persistent connection is
                          to be maintained.";
                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.";
              } // container persistent
            } // case persistent-connection
            case periodic-connection {
              container periodic {
                must 'not (../../endpoints/endpoint/ssh/'
                           + 'tcp-client-parameters/keepalives '
                           + 'or ../../endpoints/endpoint/ssh/'
                           + 'ssh-server-parameters/keepalives '
                           + 'or ../../endpoints/endpoint/tls/'
                           + 'tcp-client-parameters/keepalives '
                           + 'or ../../endpoints/endpoint/tls/'
                           + 'tls-server-parameters/keepalives)';
                presence "Indicates that a periodic connection is
                          to be maintained.";
                description
                  "Periodically connect to the NETCONF client.  The
                   NETCONF client should close the underlying TLS
                   connection upon completing planned activities.

                   This connection type increases resource
                   utilization, albeit with increased delay in
                   NETCONF client to NETCONF client interactions.";
                leaf period {
                  type uint16;
                  units "minutes";
                  default "60";
                  description
                    "Duration of time between periodic connections.";
                }
                leaf anchor-time {
                  type yang:date-and-time {
                    // constrained to minute-level granularity
                    pattern '\d{4}-\d{2}-\d{2}T\d{2}:\d{2}'
                          + '(Z|[\+\-]\d{2}:\d{2})';
                  }
                  description
                    "Designates a timestamp before or after which a
                     series of periodic connections are determined.
                     The periodic connections occur at a whole
                     multiple interval from the anchor time.  For
                     example, for an anchor time is 15 minutes past
                     midnight and a period interval of 24 hours, then
                     a periodic connection will occur 15 minutes past
                     midnight everyday.";
                }
                leaf idle-timeout {
                  type uint16;
                  units "seconds";
                  default 120; // two minutes
                  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.";
                }
              } // container periodic
            } // case periodic-connection
          } // choice connection-type
        } // container connection-type
        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
                   endpoint connected to across reboots.";
              }
              enum random-selection {
                description
                  "Indicates that reconnections should start with
                   a random endpoint.";
              }
            }
            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).";
          }
        } // container reconnect-strategy
      } // list netconf-client
    } // container call-home
  } // grouping netconf-server-grouping

  // Protocol accessible node, for servers that implement this
  // module.

  container netconf-server {
    uses netconf-server-grouping;
    description
      "Top-level container for NETCONF server configuration.";
  }
}
<CODE ENDS>

5. Design Considerations

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

5.1. 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.

5.2. 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.

5.3. 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.

5.4. 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.

5.5. 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]), 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.

5.6. For Call Home connections

The following objectives only pertain to call home connections.

5.6.1. 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.

5.6.2. 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.

5.6.3. 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.

5.6.4. 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.

5.6.5. 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.

5.6.6. 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.

5.6.7. 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).

6. Security Considerations

The YANG module defined in this document uses groupings defined in [I-D.kwatsen-netconf-tcp-client-server], [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 modules defined in this document are designed to be accessed via YANG based management protocols, such as NETCONF [RFC6241] and RESTCONF [RFC8040]. Both of these protocols have mandatory-to-implement secure transport layers (e.g., SSH, TLS) with mutual authentication.

The NETCONF access control model (NACM) [RFC8341] 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 the YANG modules that are writable/creatable/deletable (i.e., config true, which is the default). Some of 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 of the subtrees or data nodes in the modules defined in this document need to be protected from write operations.

Some of the readable data nodes in the YANG modules 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 of the subtrees or data nodes in the modules defined in this document need to be protected from read operations.

Some of the RPC operations in the YANG modules 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:

The modules defined in this document do not define any 'RPC' or 'action' statements.

7. IANA Considerations

7.1. The IETF XML Registry

This document registers two URIs in the "ns" subregistry of 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.

7.2. The YANG Module Names Registry

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

8. References

8.1. Normative References

[I-D.ietf-netconf-keystore] Watsen, K., "YANG Data Model for a Centralized Keystore Mechanism", Internet-Draft draft-ietf-netconf-keystore-08, March 2019.
[I-D.ietf-netconf-ssh-client-server] Watsen, K., Wu, G. and L. Xia, "YANG Groupings for SSH Clients and SSH Servers", Internet-Draft draft-ietf-netconf-ssh-client-server-11, March 2019.
[I-D.ietf-netconf-tls-client-server] Watsen, K., Wu, G. and L. Xia, "YANG Groupings for TLS Clients and TLS Servers", Internet-Draft draft-ietf-netconf-tls-client-server-10, March 2019.
[I-D.kwatsen-netconf-tcp-client-server] Watsen, K., "YANG Groupings for TCP Clients and TCP Servers", Internet-Draft draft-kwatsen-netconf-tcp-client-server-00, March 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010.
[RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J. and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011.
[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011.
[RFC6991] Schoenwaelder, J., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, July 2013.
[RFC7407] Bjorklund, M. and J. Schoenwaelder, "A YANG Data Model for SNMP Configuration", RFC 7407, DOI 10.17487/RFC7407, December 2014.
[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.
[RFC7950] Bjorklund, M., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.

8.2. Informative References

[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004.
[RFC8040] Bierman, A., Bjorklund, M. and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017.
[RFC8071] Watsen, K., "NETCONF Call Home and RESTCONF Call Home", RFC 8071, DOI 10.17487/RFC8071, February 2017.
[RFC8340] Bjorklund, M. and L. Berger, "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018.
[RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, March 2018.

Appendix A. Expanded Tree Diagrams

A.1. Expanded Tree Diagram for 'ietf-netconf-client'

The following tree diagram [RFC8340] provides an overview of the data model for the "ietf-netconf-client" module.

This tree diagram shows all the nodes defined in this module, including those defined by "grouping" statements used by this module.

Please see Section 3.1 for a tree diagram that illustrates what the module looks like without all the "grouping" statements expanded.

=========== NOTE: '\' line wrapping per BCP XX (RFC XXXX) ===========

module: ietf-netconf-client
  +--rw netconf-client
     +--rw initiate! {initiate}?
     |  +--rw netconf-server* [name]
     |     +--rw name                  string
     |     +--rw endpoints
     |     |  +--rw endpoint* [name]
     |     |     +--rw name         string
     |     |     +--rw (transport)
     |     |        +--:(ssh) {ssh-initiate}?
     |     |        |  +--rw ssh
     |     |        |     +--rw tcp-client-parameters
     |     |        |     |  +--rw remote-address    inet:host
     |     |        |     |  +--rw remote-port?      inet:port-number
     |     |        |     |  +--rw local-address?    inet:ip-address
     |     |        |     |  +--rw local-port?       inet:port-number
     |     |        |     |  +--rw keepalives!
     |     |        |     |          {tcp-client-keepalives}?
     |     |        |     |     +--rw idle-time         uint16
     |     |        |     |     +--rw max-probes?       uint16
     |     |        |     |     +--rw probe-interval?   uint16
     |     |        |     +--rw ssh-client-parameters
     |     |        |        +--rw client-identity
     |     |        |        |  +--rw username?            string
     |     |        |        |  +--rw (auth-type)
     |     |        |        |     +--:(password)
     |     |        |        |     |  +--rw password?      string
     |     |        |        |     +--:(public-key)
     |     |        |        |     |  +--rw public-key
     |     |        |        |     |     +--rw (local-or-keystore)
     |     |        |        |     |        +--:(local)
     |     |        |        |     |        |        {local-keys-sup\
ported}?
     |     |        |        |     |        |  +--rw local-definition
     |     |        |        |     |        |     +--rw algorithm?
     |     |        |        |     |        |     |       asymmetric\
-key-algorithm-ref
     |     |        |        |     |        |     +--rw public-key?
     |     |        |        |     |        |     |       binary
     |     |        |        |     |        |     +--rw private-key?
     |     |        |        |     |        |     |       union
     |     |        |        |     |        |     +---x generate-hid\
den-key
     |     |        |        |     |        |     |  +---w input
     |     |        |        |     |        |     |     +---w algori\
thm
     |     |        |        |     |        |     |             asym\
metric-key-algorithm-ref
     |     |        |        |     |        |     +---x install-hidd\
en-key
     |     |        |        |     |        |        +---w input
     |     |        |        |     |        |           +---w algori\
thm
     |     |        |        |     |        |           |       asym\
metric-key-algorithm-ref
     |     |        |        |     |        |           +---w public\
-key?
     |     |        |        |     |        |           |       bina\
ry
     |     |        |        |     |        |           +---w privat\
e-key?
     |     |        |        |     |        |                   bina\
ry
     |     |        |        |     |        +--:(keystore)
     |     |        |        |     |                 {keystore-suppo\
rted}?
     |     |        |        |     |           +--rw keystore-refere\
nce?
     |     |        |        |     |                   ks:asymmetric\
-key-ref
     |     |        |        |     +--:(certificate)
     |     |        |        |        +--rw certificate
     |     |        |        |                {sshcmn:ssh-x509-certs\
}?
     |     |        |        |           +--rw (local-or-keystore)
     |     |        |        |              +--:(local)
     |     |        |        |              |        {local-keys-sup\
ported}?
     |     |        |        |              |  +--rw local-definition
     |     |        |        |              |     +--rw algorithm?
     |     |        |        |              |     |       asymmetric\
-key-algorithm-ref
     |     |        |        |              |     +--rw public-key?
     |     |        |        |              |     |       binary
     |     |        |        |              |     +--rw private-key?
     |     |        |        |              |     |       union
     |     |        |        |              |     +---x generate-hid\
den-key
     |     |        |        |              |     |  +---w input
     |     |        |        |              |     |     +---w algori\
thm
     |     |        |        |              |     |             asym\
metric-key-algorithm-ref
     |     |        |        |              |     +---x install-hidd\
en-key
     |     |        |        |              |     |  +---w input
     |     |        |        |              |     |     +---w algori\
thm
     |     |        |        |              |     |     |       asym\
metric-key-algorithm-ref
     |     |        |        |              |     |     +---w public\
-key?
     |     |        |        |              |     |     |       bina\
ry
     |     |        |        |              |     |     +---w privat\
e-key?
     |     |        |        |              |     |             bina\
ry
     |     |        |        |              |     +--rw cert?
     |     |        |        |              |     |       end-entity\
-cert-cms
     |     |        |        |              |     +---n certificate-\
expiration
     |     |        |        |              |        +-- expiration-\
date
     |     |        |        |              |                yang:da\
te-and-time
     |     |        |        |              +--:(keystore)
     |     |        |        |                       {keystore-suppo\
rted}?
     |     |        |        |                 +--rw keystore-refere\
nce?
     |     |        |        |                         ks:asymmetric\
-key-certificate-ref
     |     |        |        +--rw server-authentication
     |     |        |        |  +--rw pinned-ssh-host-keys?
     |     |        |        |  |       ta:pinned-host-keys-ref
     |     |        |        |  |       {ta:ssh-host-keys}?
     |     |        |        |  +--rw pinned-ca-certs?
     |     |        |        |  |       ta:pinned-certificates-ref
     |     |        |        |  |       {sshcmn:ssh-x509-certs,ta:x5\
09-certificates}?
     |     |        |        |  +--rw pinned-server-certs?
     |     |        |        |          ta:pinned-certificates-ref
     |     |        |        |          {sshcmn:ssh-x509-certs,ta:x5\
09-certificates}?
     |     |        |        +--rw transport-params
     |     |        |        |       {ssh-client-transport-params-co\
nfig}?
     |     |        |        |  +--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 keepalives!
     |     |        |                {ssh-client-keepalives}?
     |     |        |           +--rw max-wait?       uint16
     |     |        |           +--rw max-attempts?   uint8
     |     |        +--:(tls) {tls-initiate}?
     |     |           +--rw tls
     |     |              +--rw tcp-client-parameters
     |     |              |  +--rw remote-address    inet:host
     |     |              |  +--rw remote-port?      inet:port-number
     |     |              |  +--rw local-address?    inet:ip-address
     |     |              |  +--rw local-port?       inet:port-number
     |     |              |  +--rw keepalives!
     |     |              |          {tcp-client-keepalives}?
     |     |              |     +--rw idle-time         uint16
     |     |              |     +--rw max-probes?       uint16
     |     |              |     +--rw probe-interval?   uint16
     |     |              +--rw tls-client-parameters
     |     |                 +--rw client-identity
     |     |                 |  +--rw (auth-type)
     |     |                 |     +--:(certificate)
     |     |                 |        +--rw certificate
     |     |                 |           +--rw (local-or-keystore)
     |     |                 |              +--:(local)
     |     |                 |              |        {local-keys-sup\
ported}?
     |     |                 |              |  +--rw local-definition
     |     |                 |              |     +--rw algorithm?
     |     |                 |              |     |       asymmetric\
-key-algorithm-ref
     |     |                 |              |     +--rw public-key?
     |     |                 |              |     |       binary
     |     |                 |              |     +--rw private-key?
     |     |                 |              |     |       union
     |     |                 |              |     +---x generate-hid\
den-key
     |     |                 |              |     |  +---w input
     |     |                 |              |     |     +---w algori\
thm
     |     |                 |              |     |             asym\
metric-key-algorithm-ref
     |     |                 |              |     +---x install-hidd\
en-key
     |     |                 |              |     |  +---w input
     |     |                 |              |     |     +---w algori\
thm
     |     |                 |              |     |     |       asym\
metric-key-algorithm-ref
     |     |                 |              |     |     +---w public\
-key?
     |     |                 |              |     |     |       bina\
ry
     |     |                 |              |     |     +---w privat\
e-key?
     |     |                 |              |     |             bina\
ry
     |     |                 |              |     +--rw cert?
     |     |                 |              |     |       end-entity\
-cert-cms
     |     |                 |              |     +---n certificate-\
expiration
     |     |                 |              |        +-- expiration-\
date
     |     |                 |              |                yang:da\
te-and-time
     |     |                 |              +--:(keystore)
     |     |                 |                       {keystore-suppo\
rted}?
     |     |                 |                 +--rw keystore-refere\
nce?
     |     |                 |                         ks:asymmetric\
-key-certificate-ref
     |     |                 +--rw server-authentication
     |     |                 |  +--rw pinned-ca-certs?
     |     |                 |  |       ta:pinned-certificates-ref
     |     |                 |  |       {ta:x509-certificates}?
     |     |                 |  +--rw pinned-server-certs?
     |     |                 |          ta:pinned-certificates-ref
     |     |                 |          {ta:x509-certificates}?
     |     |                 +--rw hello-params
     |     |                 |       {tls-client-hello-params-config\
}?
     |     |                 |  +--rw tls-versions
     |     |                 |  |  +--rw tls-version*   identityref
     |     |                 |  +--rw cipher-suites
     |     |                 |     +--rw cipher-suite*   identityref
     |     |                 +--rw keepalives!
     |     |                         {tls-client-keepalives}?
     |     |                    +--rw max-wait?       uint16
     |     |                    +--rw max-attempts?   uint8
     |     +--rw connection-type
     |     |  +--rw (connection-type)
     |     |     +--:(persistent-connection)
     |     |     |  +--rw persistent!
     |     |     +--:(periodic-connection)
     |     |        +--rw periodic!
     |     |           +--rw period?         uint16
     |     |           +--rw anchor-time?    yang:date-and-time
     |     |           +--rw idle-timeout?   uint16
     |     +--rw reconnect-strategy
     |        +--rw start-with?     enumeration
     |        +--rw max-attempts?   uint8
     +--rw listen! {listen}?
        +--rw idle-timeout?   uint16
        +--rw endpoint* [name]
           +--rw name         string
           +--rw (transport)
              +--:(ssh) {ssh-listen}?
              |  +--rw ssh
              |     +--rw tcp-server-parameters
              |     |  +--rw local-address    inet:ip-address
              |     |  +--rw local-port?      inet:port-number
              |     |  +--rw keepalives! {tcp-server-keepalives}?
              |     |     +--rw idle-time         uint16
              |     |     +--rw max-probes?       uint16
              |     |     +--rw probe-interval?   uint16
              |     +--rw ssh-client-parameters
              |        +--rw client-identity
              |        |  +--rw username?            string
              |        |  +--rw (auth-type)
              |        |     +--:(password)
              |        |     |  +--rw password?      string
              |        |     +--:(public-key)
              |        |     |  +--rw public-key
              |        |     |     +--rw (local-or-keystore)
              |        |     |        +--:(local)
              |        |     |        |        {local-keys-supported\
}?
              |        |     |        |  +--rw local-definition
              |        |     |        |     +--rw algorithm?
              |        |     |        |     |       asymmetric-key-a\
lgorithm-ref
              |        |     |        |     +--rw public-key?
              |        |     |        |     |       binary
              |        |     |        |     +--rw private-key?
              |        |     |        |     |       union
              |        |     |        |     +---x generate-hidden-key
              |        |     |        |     |  +---w input
              |        |     |        |     |     +---w algorithm
              |        |     |        |     |             asymmetric\
-key-algorithm-ref
              |        |     |        |     +---x install-hidden-key
              |        |     |        |        +---w input
              |        |     |        |           +---w algorithm
              |        |     |        |           |       asymmetric\
-key-algorithm-ref
              |        |     |        |           +---w public-key?
              |        |     |        |           |       binary
              |        |     |        |           +---w private-key?
              |        |     |        |                   binary
              |        |     |        +--:(keystore)
              |        |     |                 {keystore-supported}?
              |        |     |           +--rw keystore-reference?
              |        |     |                   ks:asymmetric-key-r\
ef
              |        |     +--:(certificate)
              |        |        +--rw certificate
              |        |                {sshcmn:ssh-x509-certs}?
              |        |           +--rw (local-or-keystore)
              |        |              +--:(local)
              |        |              |        {local-keys-supported\
}?
              |        |              |  +--rw local-definition
              |        |              |     +--rw algorithm?
              |        |              |     |       asymmetric-key-a\
lgorithm-ref
              |        |              |     +--rw public-key?
              |        |              |     |       binary
              |        |              |     +--rw private-key?
              |        |              |     |       union
              |        |              |     +---x generate-hidden-key
              |        |              |     |  +---w input
              |        |              |     |     +---w algorithm
              |        |              |     |             asymmetric\
-key-algorithm-ref
              |        |              |     +---x install-hidden-key
              |        |              |     |  +---w input
              |        |              |     |     +---w algorithm
              |        |              |     |     |       asymmetric\
-key-algorithm-ref
              |        |              |     |     +---w public-key?
              |        |              |     |     |       binary
              |        |              |     |     +---w private-key?
              |        |              |     |             binary
              |        |              |     +--rw cert?
              |        |              |     |       end-entity-cert-\
cms
              |        |              |     +---n certificate-expira\
tion
              |        |              |        +-- expiration-date
              |        |              |                yang:date-and\
-time
              |        |              +--:(keystore)
              |        |                       {keystore-supported}?
              |        |                 +--rw keystore-reference?
              |        |                         ks:asymmetric-key-c\
ertificate-ref
              |        +--rw server-authentication
              |        |  +--rw pinned-ssh-host-keys?
              |        |  |       ta:pinned-host-keys-ref
              |        |  |       {ta:ssh-host-keys}?
              |        |  +--rw pinned-ca-certs?
              |        |  |       ta:pinned-certificates-ref
              |        |  |       {sshcmn:ssh-x509-certs,ta:x509-cer\
tificates}?
              |        |  +--rw pinned-server-certs?
              |        |          ta:pinned-certificates-ref
              |        |          {sshcmn:ssh-x509-certs,ta:x509-cer\
tificates}?
              |        +--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 keepalives! {ssh-client-keepalives}?
              |           +--rw max-wait?       uint16
              |           +--rw max-attempts?   uint8
              +--:(tls) {tls-listen}?
                 +--rw tls
                    +--rw tcp-server-parameters
                    |  +--rw local-address    inet:ip-address
                    |  +--rw local-port?      inet:port-number
                    |  +--rw keepalives! {tcp-server-keepalives}?
                    |     +--rw idle-time         uint16
                    |     +--rw max-probes?       uint16
                    |     +--rw probe-interval?   uint16
                    +--rw tls-client-parameters
                       +--rw client-identity
                       |  +--rw (auth-type)
                       |     +--:(certificate)
                       |        +--rw certificate
                       |           +--rw (local-or-keystore)
                       |              +--:(local)
                       |              |        {local-keys-supported\
}?
                       |              |  +--rw local-definition
                       |              |     +--rw algorithm?
                       |              |     |       asymmetric-key-a\
lgorithm-ref
                       |              |     +--rw public-key?
                       |              |     |       binary
                       |              |     +--rw private-key?
                       |              |     |       union
                       |              |     +---x generate-hidden-key
                       |              |     |  +---w input
                       |              |     |     +---w algorithm
                       |              |     |             asymmetric\
-key-algorithm-ref
                       |              |     +---x install-hidden-key
                       |              |     |  +---w input
                       |              |     |     +---w algorithm
                       |              |     |     |       asymmetric\
-key-algorithm-ref
                       |              |     |     +---w public-key?
                       |              |     |     |       binary
                       |              |     |     +---w private-key?
                       |              |     |             binary
                       |              |     +--rw cert?
                       |              |     |       end-entity-cert-\
cms
                       |              |     +---n certificate-expira\
tion
                       |              |        +-- expiration-date
                       |              |                yang:date-and\
-time
                       |              +--:(keystore)
                       |                       {keystore-supported}?
                       |                 +--rw keystore-reference?
                       |                         ks:asymmetric-key-c\
ertificate-ref
                       +--rw server-authentication
                       |  +--rw pinned-ca-certs?
                       |  |       ta:pinned-certificates-ref
                       |  |       {ta:x509-certificates}?
                       |  +--rw pinned-server-certs?
                       |          ta:pinned-certificates-ref
                       |          {ta:x509-certificates}?
                       +--rw hello-params
                       |       {tls-client-hello-params-config}?
                       |  +--rw tls-versions
                       |  |  +--rw tls-version*   identityref
                       |  +--rw cipher-suites
                       |     +--rw cipher-suite*   identityref
                       +--rw keepalives! {tls-client-keepalives}?
                          +--rw max-wait?       uint16
                          +--rw max-attempts?   uint8

A.2. Expanded Tree Diagram for 'ietf-netconf-server'

The following tree diagram [RFC8340] provides an overview of the data model for the "ietf-netconf-server" module.

This tree diagram shows all the nodes defined in this module, including those defined by "grouping" statements used by this module.

Please see Section 4.1 for a tree diagram that illustrates what the module looks like without all the "grouping" statements expanded.

=========== NOTE: '\' line wrapping per BCP XX (RFC XXXX) ===========

module: ietf-netconf-server
  +--rw netconf-server
     +--rw listen! {listen}?
     |  +--rw idle-timeout?   uint16
     |  +--rw endpoint* [name]
     |     +--rw name         string
     |     +--rw (transport)
     |        +--:(ssh) {ssh-listen}?
     |        |  +--rw ssh
     |        |     +--rw tcp-server-parameters
     |        |     |  +--rw local-address    inet:ip-address
     |        |     |  +--rw local-port?      inet:port-number
     |        |     |  +--rw keepalives! {tcp-server-keepalives}?
     |        |     |     +--rw idle-time         uint16
     |        |     |     +--rw max-probes?       uint16
     |        |     |     +--rw probe-interval?   uint16
     |        |     +--rw ssh-server-parameters
     |        |        +--rw server-identity
     |        |        |  +--rw host-key* [name]
     |        |        |     +--rw name                 string
     |        |        |     +--rw (host-key-type)
     |        |        |        +--:(public-key)
     |        |        |        |  +--rw public-key
     |        |        |        |     +--rw (local-or-keystore)
     |        |        |        |        +--:(local)
     |        |        |        |        |        {local-keys-suppor\
ted}?
     |        |        |        |        |  +--rw local-definition
     |        |        |        |        |     +--rw algorithm?
     |        |        |        |        |     |       asymmetric-ke\
y-algorithm-ref
     |        |        |        |        |     +--rw public-key?
     |        |        |        |        |     |       binary
     |        |        |        |        |     +--rw private-key?
     |        |        |        |        |     |       union
     |        |        |        |        |     +---x generate-hidden\
-key
     |        |        |        |        |     |  +---w input
     |        |        |        |        |     |     +---w algorithm
     |        |        |        |        |     |             asymmet\
ric-key-algorithm-ref
     |        |        |        |        |     +---x install-hidden-\
key
     |        |        |        |        |        +---w input
     |        |        |        |        |           +---w algorithm
     |        |        |        |        |           |       asymmet\
ric-key-algorithm-ref
     |        |        |        |        |           +---w public-ke\
y?
     |        |        |        |        |           |       binary
     |        |        |        |        |           +---w private-k\
ey?
     |        |        |        |        |                   binary
     |        |        |        |        +--:(keystore)
     |        |        |        |                 {keystore-supporte\
d}?
     |        |        |        |           +--rw keystore-reference?
     |        |        |        |                   ks:asymmetric-ke\
y-ref
     |        |        |        +--:(certificate)
     |        |        |           +--rw certificate
     |        |        |                   {sshcmn:ssh-x509-certs}?
     |        |        |              +--rw (local-or-keystore)
     |        |        |                 +--:(local)
     |        |        |                 |        {local-keys-suppor\
ted}?
     |        |        |                 |  +--rw local-definition
     |        |        |                 |     +--rw algorithm?
     |        |        |                 |     |       asymmetric-ke\
y-algorithm-ref
     |        |        |                 |     +--rw public-key?
     |        |        |                 |     |       binary
     |        |        |                 |     +--rw private-key?
     |        |        |                 |     |       union
     |        |        |                 |     +---x generate-hidden\
-key
     |        |        |                 |     |  +---w input
     |        |        |                 |     |     +---w algorithm
     |        |        |                 |     |             asymmet\
ric-key-algorithm-ref
     |        |        |                 |     +---x install-hidden-\
key
     |        |        |                 |     |  +---w input
     |        |        |                 |     |     +---w algorithm
     |        |        |                 |     |     |       asymmet\
ric-key-algorithm-ref
     |        |        |                 |     |     +---w public-ke\
y?
     |        |        |                 |     |     |       binary
     |        |        |                 |     |     +---w private-k\
ey?
     |        |        |                 |     |             binary
     |        |        |                 |     +--rw cert?
     |        |        |                 |     |       end-entity-ce\
rt-cms
     |        |        |                 |     +---n certificate-exp\
iration
     |        |        |                 |        +-- expiration-date
     |        |        |                 |                yang:date-\
and-time
     |        |        |                 +--:(keystore)
     |        |        |                          {keystore-supporte\
d}?
     |        |        |                    +--rw keystore-reference?
     |        |        |                            ks:asymmetric-ke\
y-certificate-ref
     |        |        +--rw client-cert-auth
     |        |        |       {sshcmn:ssh-x509-certs}?
     |        |        |  +--rw pinned-ca-certs?
     |        |        |  |       ta:pinned-certificates-ref
     |        |        |  |       {ta:x509-certificates}?
     |        |        |  +--rw pinned-client-certs?
     |        |        |          ta:pinned-certificates-ref
     |        |        |          {ta:x509-certificates}?
     |        |        +--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 keepalives! {ssh-server-keepalives}?
     |        |           +--rw max-wait?       uint16
     |        |           +--rw max-attempts?   uint8
     |        +--:(tls) {tls-listen}?
     |           +--rw tls
     |              +--rw tcp-server-parameters
     |              |  +--rw local-address    inet:ip-address
     |              |  +--rw local-port?      inet:port-number
     |              |  +--rw keepalives! {tcp-server-keepalives}?
     |              |     +--rw idle-time         uint16
     |              |     +--rw max-probes?       uint16
     |              |     +--rw probe-interval?   uint16
     |              +--rw tls-server-parameters
     |                 +--rw server-identity
     |                 |  +--rw (local-or-keystore)
     |                 |     +--:(local) {local-keys-supported}?
     |                 |     |  +--rw local-definition
     |                 |     |     +--rw algorithm?
     |                 |     |     |       asymmetric-key-algorithm-\
ref
     |                 |     |     +--rw public-key?
     |                 |     |     |       binary
     |                 |     |     +--rw private-key?
     |                 |     |     |       union
     |                 |     |     +---x generate-hidden-key
     |                 |     |     |  +---w input
     |                 |     |     |     +---w algorithm
     |                 |     |     |             asymmetric-key-algo\
rithm-ref
     |                 |     |     +---x install-hidden-key
     |                 |     |     |  +---w input
     |                 |     |     |     +---w algorithm
     |                 |     |     |     |       asymmetric-key-algo\
rithm-ref
     |                 |     |     |     +---w public-key?    binary
     |                 |     |     |     +---w private-key?   binary
     |                 |     |     +--rw cert?
     |                 |     |     |       end-entity-cert-cms
     |                 |     |     +---n certificate-expiration
     |                 |     |        +-- expiration-date
     |                 |     |                yang:date-and-time
     |                 |     +--:(keystore) {keystore-supported}?
     |                 |        +--rw keystore-reference?
     |                 |                ks:asymmetric-key-certificat\
e-ref
     |                 +--rw client-authentication
     |                 |  +--rw pinned-ca-certs?
     |                 |  |       ta:pinned-certificates-ref
     |                 |  |       {ta:x509-certificates}?
     |                 |  +--rw pinned-client-certs?
     |                 |  |       ta:pinned-certificates-ref
     |                 |  |       {ta:x509-certificates}?
     |                 |  +--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 keepalives! {tls-server-keepalives}?
     |                    +--rw max-wait?       uint16
     |                    +--rw max-attempts?   uint8
     +--rw call-home! {call-home}?
        +--rw netconf-client* [name]
           +--rw name                  string
           +--rw endpoints
           |  +--rw endpoint* [name]
           |     +--rw name         string
           |     +--rw (transport)
           |        +--:(ssh) {ssh-call-home}?
           |        |  +--rw ssh
           |        |     +--rw tcp-client-parameters
           |        |     |  +--rw remote-address    inet:host
           |        |     |  +--rw remote-port?      inet:port-number
           |        |     |  +--rw local-address?    inet:ip-address
           |        |     |  +--rw local-port?       inet:port-number
           |        |     |  +--rw keepalives!
           |        |     |          {tcp-client-keepalives}?
           |        |     |     +--rw idle-time         uint16
           |        |     |     +--rw max-probes?       uint16
           |        |     |     +--rw probe-interval?   uint16
           |        |     +--rw ssh-server-parameters
           |        |        +--rw server-identity
           |        |        |  +--rw host-key* [name]
           |        |        |     +--rw name                 string
           |        |        |     +--rw (host-key-type)
           |        |        |        +--:(public-key)
           |        |        |        |  +--rw public-key
           |        |        |        |     +--rw (local-or-keystore)
           |        |        |        |        +--:(local)
           |        |        |        |        |        {local-keys-\
supported}?
           |        |        |        |        |  +--rw local-defini\
tion
           |        |        |        |        |     +--rw algorithm?
           |        |        |        |        |     |       asymmet\
ric-key-algorithm-ref
           |        |        |        |        |     +--rw public-ke\
y?
           |        |        |        |        |     |       binary
           |        |        |        |        |     +--rw private-k\
ey?
           |        |        |        |        |     |       union
           |        |        |        |        |     +---x generate-\
hidden-key
           |        |        |        |        |     |  +---w input
           |        |        |        |        |     |     +---w alg\
orithm
           |        |        |        |        |     |             a\
symmetric-key-algorithm-ref
           |        |        |        |        |     +---x install-h\
idden-key
           |        |        |        |        |        +---w input
           |        |        |        |        |           +---w alg\
orithm
           |        |        |        |        |           |       a\
symmetric-key-algorithm-ref
           |        |        |        |        |           +---w pub\
lic-key?
           |        |        |        |        |           |       b\
inary
           |        |        |        |        |           +---w pri\
vate-key?
           |        |        |        |        |                   b\
inary
           |        |        |        |        +--:(keystore)
           |        |        |        |                 {keystore-su\
pported}?
           |        |        |        |           +--rw keystore-ref\
erence?
           |        |        |        |                   ks:asymmet\
ric-key-ref
           |        |        |        +--:(certificate)
           |        |        |           +--rw certificate
           |        |        |                   {sshcmn:ssh-x509-ce\
rts}?
           |        |        |              +--rw (local-or-keystore)
           |        |        |                 +--:(local)
           |        |        |                 |        {local-keys-\
supported}?
           |        |        |                 |  +--rw local-defini\
tion
           |        |        |                 |     +--rw algorithm?
           |        |        |                 |     |       asymmet\
ric-key-algorithm-ref
           |        |        |                 |     +--rw public-ke\
y?
           |        |        |                 |     |       binary
           |        |        |                 |     +--rw private-k\
ey?
           |        |        |                 |     |       union
           |        |        |                 |     +---x generate-\
hidden-key
           |        |        |                 |     |  +---w input
           |        |        |                 |     |     +---w alg\
orithm
           |        |        |                 |     |             a\
symmetric-key-algorithm-ref
           |        |        |                 |     +---x install-h\
idden-key
           |        |        |                 |     |  +---w input
           |        |        |                 |     |     +---w alg\
orithm
           |        |        |                 |     |     |       a\
symmetric-key-algorithm-ref
           |        |        |                 |     |     +---w pub\
lic-key?
           |        |        |                 |     |     |       b\
inary
           |        |        |                 |     |     +---w pri\
vate-key?
           |        |        |                 |     |             b\
inary
           |        |        |                 |     +--rw cert?
           |        |        |                 |     |       end-ent\
ity-cert-cms
           |        |        |                 |     +---n certifica\
te-expiration
           |        |        |                 |        +-- expirati\
on-date
           |        |        |                 |                yang\
:date-and-time
           |        |        |                 +--:(keystore)
           |        |        |                          {keystore-su\
pported}?
           |        |        |                    +--rw keystore-ref\
erence?
           |        |        |                            ks:asymmet\
ric-key-certificate-ref
           |        |        +--rw client-cert-auth
           |        |        |       {sshcmn:ssh-x509-certs}?
           |        |        |  +--rw pinned-ca-certs?
           |        |        |  |       ta:pinned-certificates-ref
           |        |        |  |       {ta:x509-certificates}?
           |        |        |  +--rw pinned-client-certs?
           |        |        |          ta:pinned-certificates-ref
           |        |        |          {ta:x509-certificates}?
           |        |        +--rw transport-params
           |        |        |       {ssh-server-transport-params-co\
nfig}?
           |        |        |  +--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 keepalives!
           |        |                {ssh-server-keepalives}?
           |        |           +--rw max-wait?       uint16
           |        |           +--rw max-attempts?   uint8
           |        +--:(tls) {tls-call-home}?
           |           +--rw tls
           |              +--rw tcp-client-parameters
           |              |  +--rw remote-address    inet:host
           |              |  +--rw remote-port?      inet:port-number
           |              |  +--rw local-address?    inet:ip-address
           |              |  +--rw local-port?       inet:port-number
           |              |  +--rw keepalives!
           |              |          {tcp-client-keepalives}?
           |              |     +--rw idle-time         uint16
           |              |     +--rw max-probes?       uint16
           |              |     +--rw probe-interval?   uint16
           |              +--rw tls-server-parameters
           |                 +--rw server-identity
           |                 |  +--rw (local-or-keystore)
           |                 |     +--:(local)
           |                 |     |        {local-keys-supported}?
           |                 |     |  +--rw local-definition
           |                 |     |     +--rw algorithm?
           |                 |     |     |       asymmetric-key-algo\
rithm-ref
           |                 |     |     +--rw public-key?
           |                 |     |     |       binary
           |                 |     |     +--rw private-key?
           |                 |     |     |       union
           |                 |     |     +---x generate-hidden-key
           |                 |     |     |  +---w input
           |                 |     |     |     +---w algorithm
           |                 |     |     |             asymmetric-ke\
y-algorithm-ref
           |                 |     |     +---x install-hidden-key
           |                 |     |     |  +---w input
           |                 |     |     |     +---w algorithm
           |                 |     |     |     |       asymmetric-ke\
y-algorithm-ref
           |                 |     |     |     +---w public-key?
           |                 |     |     |     |       binary
           |                 |     |     |     +---w private-key?
           |                 |     |     |             binary
           |                 |     |     +--rw cert?
           |                 |     |     |       end-entity-cert-cms
           |                 |     |     +---n certificate-expiration
           |                 |     |        +-- expiration-date
           |                 |     |                yang:date-and-ti\
me
           |                 |     +--:(keystore)
           |                 |              {keystore-supported}?
           |                 |        +--rw keystore-reference?
           |                 |                ks:asymmetric-key-cert\
ificate-ref
           |                 +--rw client-authentication
           |                 |  +--rw pinned-ca-certs?
           |                 |  |       ta:pinned-certificates-ref
           |                 |  |       {ta:x509-certificates}?
           |                 |  +--rw pinned-client-certs?
           |                 |  |       ta:pinned-certificates-ref
           |                 |  |       {ta:x509-certificates}?
           |                 |  +--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 keepalives!
           |                         {tls-server-keepalives}?
           |                    +--rw max-wait?       uint16
           |                    +--rw max-attempts?   uint8
           +--rw connection-type
           |  +--rw (connection-type)
           |     +--:(persistent-connection)
           |     |  +--rw persistent!
           |     +--:(periodic-connection)
           |        +--rw periodic!
           |           +--rw period?         uint16
           |           +--rw anchor-time?    yang:date-and-time
           |           +--rw idle-timeout?   uint16
           +--rw reconnect-strategy
              +--rw start-with?     enumeration
              +--rw max-attempts?   uint8

Appendix B. Change Log

B.1. 00 to 01

B.2. 01 to 02

B.3. 02 to 03

B.4. 03 to 04

B.5. 04 to 05

B.6. 05 to 06

B.7. 06 to 07

B.8. 07 to 08

B.9. 08 to 09

B.10. 09 to 10

B.11. 10 to 11

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, Ramkumar Dhanapal, Mehmet Ersue, Balázs Kovács, David Lamparter, Alan Luchuk, Ladislav Lhotka, Radek Krejci, Tom Petch, Juergen Schoenwaelder, Phil Shafer, Sean Turner, and Bert Wijnen.

Author's Address

Kent Watsen Watsen Networks EMail: kent+ietf@watsen.net