NETCONF Working Group K. Watsen
Internet-Draft Juniper Networks
Intended status: Standards Track G. Wu
Expires: December 15, 2017 Cisco Networks
J. Schoenwaelder
Jacobs University Bremen
June 13, 2017

NETCONF Client and Server Models
draft-ietf-netconf-netconf-client-server-03

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

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Copyright Notice

Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.

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


Table of Contents

1. Introduction

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

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

1.1. Terminology

The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].

1.2. Tree Diagrams

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

2. The NETCONF Client Model

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

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

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

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

2.1. Tree Diagram

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

module: ietf-netconf-client
  groupings:
  netconf-client
      +---- initiate {initiate}?
      |  +---- netconf-server* [name]
      |     +---- name?                 string
      |     +---- (transport)
      |     |  +--:(ssh) {ssh-initiate}?
      |     |  |  +---- ssh
      |     |  |     +---- endpoints
      |     |  |     |  +---- endpoint* [name]
      |     |  |     |     +---- name?      string
      |     |  |     |     +---- address    inet:host
      |     |  |     |     +---- port?      inet:port-number
      |     |  |     +---- server-auth
      |     |  |     |  +---- trusted-ssh-host-keys?
      |     |  |     |  |       -> /ks:keystore/trusted-host-keys/name
      |     |  |     |  +---- trusted-ca-certs?        leafref
      |     |  |     |  |       {sshcom:ssh-x509-certs}?
      |     |  |     |  +---- trusted-server-certs?    leafref
      |     |  |     |          {sshcom:ssh-x509-certs}?
      |     |  |     +---- client-auth
      |     |  |     |  +---- username?      string
      |     |  |     |  +---- (auth-type)?
      |     |  |     |     +--:(certificate)
      |     |  |     |     |  +---- certificate?   leafref
      |     |  |     |     |          {sshcom:ssh-x509-certs}?
      |     |  |     |     +--:(public-key)
      |     |  |     |     |  +---- public-key?
      |     |  |     |     |          -> /ks:keystore/keys/key/name
      |     |  |     |     +--:(password)
      |     |  |     |        +---- password?      string
      |     |  |     +---- transport-params
      |     |  |             {ssh-client-transport-params-config}?
      |     |  |        +---- host-key
      |     |  |        |  +---- host-key-alg*   identityref
      |     |  |        +---- key-exchange
      |     |  |        |  +---- key-exchange-alg*   identityref
      |     |  |        +---- encryption
      |     |  |        |  +---- encryption-alg*   identityref
      |     |  |        +---- mac
      |     |  |        |  +---- mac-alg*   identityref
      |     |  |        +---- compression
      |     |  |           +---- compression-alg*   identityref
      |     |  +--:(tls) {tls-initiate}?
      |     |     +---- tls
      |     |        +---- endpoints
      |     |        |  +---- endpoint* [name]
      |     |        |     +---- name?      string
      |     |        |     +---- address    inet:host
      |     |        |     +---- port?      inet:port-number
      |     |        +---- server-auth
      |     |        |  +---- trusted-ca-certs?       leafref
      |     |        |  +---- trusted-server-certs?   leafref
      |     |        +---- client-auth
      |     |        |  +---- (auth-type)?
      |     |        |     +--:(certificate)
      |     |        |        +---- certificate?   leafref
      |     |        +---- hello-params
      |     |                {tls-client-hello-params-config}?
      |     |           +---- tls-versions
      |     |           |  +---- tls-version*   identityref
      |     |           +---- cipher-suites
      |     |              +---- cipher-suite*   identityref
      |     +---- connection-type
      |     |  +---- (connection-type)?
      |     |     +--:(persistent-connection)
      |     |     |  +---- persistent!
      |     |     |     +---- idle-timeout?   uint32
      |     |     |     +---- keep-alives
      |     |     |        +---- max-wait?       uint16
      |     |     |        +---- max-attempts?   uint8
      |     |     +--:(periodic-connection)
      |     |        +---- periodic!
      |     |           +---- idle-timeout?        uint16
      |     |           +---- reconnect-timeout?   uint16
      |     +---- reconnect-strategy
      |        +---- start-with?     enumeration
      |        +---- max-attempts?   uint8
      +---- listen {listen}?
         +---- max-sessions?   uint16
         +---- idle-timeout?   uint16
         +---- endpoint* [name]
            +---- name?   string
            +---- (transport)
               +--:(ssh) {ssh-listen}?
               |  +---- ssh
               |     +---- address?            inet:ip-address
               |     +---- port?               inet:port-number
               |     +---- server-auth
               |     |  +---- trusted-ssh-host-keys?
               |     |  |       -> /ks:keystore/trusted-host-keys/name
               |     |  +---- trusted-ca-certs?        leafref
               |     |  |       {sshcom:ssh-x509-certs}?
               |     |  +---- trusted-server-certs?    leafref
               |     |          {sshcom:ssh-x509-certs}?
               |     +---- client-auth
               |     |  +---- username?      string
               |     |  +---- (auth-type)?
               |     |     +--:(certificate)
               |     |     |  +---- certificate?   leafref
               |     |     |          {sshcom:ssh-x509-certs}?
               |     |     +--:(public-key)
               |     |     |  +---- public-key?
               |     |     |          -> /ks:keystore/keys/key/name
               |     |     +--:(password)
               |     |        +---- password?      string
               |     +---- transport-params
               |             {ssh-client-transport-params-config}?
               |        +---- host-key
               |        |  +---- host-key-alg*   identityref
               |        +---- key-exchange
               |        |  +---- key-exchange-alg*   identityref
               |        +---- encryption
               |        |  +---- encryption-alg*   identityref
               |        +---- mac
               |        |  +---- mac-alg*   identityref
               |        +---- compression
               |           +---- compression-alg*   identityref
               +--:(tls) {tls-listen}?
                  +---- tls
                     +---- address?        inet:ip-address
                     +---- port?           inet:port-number
                     +---- server-auth
                     |  +---- trusted-ca-certs?       leafref
                     |  +---- trusted-server-certs?   leafref
                     +---- client-auth
                     |  +---- (auth-type)?
                     |     +--:(certificate)
                     |        +---- certificate?   leafref
                     +---- hello-params
                             {tls-client-hello-params-config}?
                        +---- tls-versions
                        |  +---- tls-version*   identityref
                        +---- cipher-suites
                           +---- cipher-suite*   identityref

  endpoints-container
      +---- endpoints
         +---- endpoint* [name]
            +---- name?      string
            +---- address    inet:host
            +---- port?      inet:port-number

2.2. Example Usage

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

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

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

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

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

2.3. YANG Model

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


<CODE BEGINS> file "ietf-netconf-client@2017-06-13.yang"

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

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

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

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

  import ietf-tls-client {
    prefix ts;
    revision-date 2017-06-13; // stable grouping definitions
    reference
      "RFC ZZZZ: TLS Client and Server Models";
  }
 
  organization
   "IETF NETCONF (Network Configuration) Working Group";

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

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

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


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

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

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

    This version of this YANG module is part of RFC XXXX; see
    the RFC itself for full legal notices.";

  revision "2017-06-13" {
    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";
  }

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

    container initiate {
      if-feature initiate;
      description
        "Configures client initiating underlying TCP connections.";
      list netconf-server {
        key name;
        description
          "List of NETCONF servers the NETCONF client is to initiate
           connections to.";
        leaf name {
          type string;
          description
            "An arbitrary name for the NETCONF server.";
        }
        choice transport {
          mandatory true;
          description
            "Selects between available transports.";

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

          case tls {
            if-feature tls-initiate;
            container tls {
              description
                "Specifies TLS-specific transport configuration.";
              uses endpoints-container {
                refine endpoints/endpoint/port {
                  default 6513;
                }
              }
              uses ts:tls-client-grouping {
                refine "client-auth" {
                  must 'certificate';
                  description
                    "NETCONF/TLS clients MUST pass a client certiticate.";
                }
              }
            }
          } // end tls

        } // end transport

        container connection-type {
          description
           "Indicates the kind of connection to use.";
          choice connection-type {
            description
              "Selects between available connection types.";
            case persistent-connection {
              container persistent {
                presence true;
                description
                 "Maintain a persistent connection to the NETCONF 
                  server. If the connection goes down, immediately 
                  start trying to reconnect to it, using the 
                  reconnection strategy.
    
                  This connection type minimizes any NETCONF server
                  to NETCONF client data-transfer delay, albeit at 
                  the expense of holding resources longer.";
                leaf idle-timeout {
                  type uint32;
                  units "seconds";
                  default 86400;  // one day;
                  description
                    "Specifies the maximum number of seconds that a 
                     a NETCONF session may remain idle. A NETCONF 
                     session will be dropped if it is idle for an 
                     interval longer than this number of seconds.  
                     If set to zero, then the client will never drop
                     a session because it is idle.  Sessions that 
                     have a notification subscription active are 
                     never dropped.";
                }
                container keep-alives {
                  description
                    "Configures the keep-alive policy, to proactively
                     test the aliveness of the SSH/TLS server.  An
                     unresponsive SSH/TLS server will be dropped after
                     approximately max-attempts * max-wait seconds.";
                  reference
                    "RFC 8071: NETCONF Call Home and RESTCONF Call
                     Home, Section 3.1, item S6";
                  leaf max-wait {
                    type uint16 {
                      range "1..max";
                    }
                    units seconds;
                    default 30;
                    description
                     "Sets the amount of time in seconds after which 
                      if no data has been received from the SSH/TLS
                      server, a SSH/TLS-level message will be sent 
                      to test the aliveness of the SSH/TLS server.";
                  }
                  leaf max-attempts {
                    type uint8;
                    default 3;
                    description
                     "Sets the maximum number of sequential keep-alive
                      messages that can fail to obtain a response from
                      the SSH/TLS server before assuming the SSH/TLS
                      server is no longer alive.";
                  }
                }
              }
            }
            case periodic-connection {
              container periodic {
                presence true;
                description
                 "Periodically connect to the NETCONF server, so that
                  the NETCONF server may deliver messages pending for
                  the NETCONF client.  The NETCONF server must close
                  the connection when it is ready to release it. Once
                  the connection has been closed, the NETCONF client
                  will restart its timer until the next connection.";
                leaf idle-timeout {
                  type uint16;
                  units "seconds";
                  default 300; // five minutes
                  description
                    "Specifies the maximum number of seconds that a 
                     a NETCONF session may remain idle. A NETCONF 
                     session will be dropped if it is idle for an 
                     interval longer than this number of seconds.  
                     If set to zero, then the server will never drop
                     a session because it is idle.  Sessions that 
                     have a notification subscription active are 
                     never dropped.";
                }
                leaf reconnect-timeout {
                  type uint16 {
                    range "1..max";
                  }
                  units minutes;
                  default 60;
                  description
                   "Sets the maximum amount of unconnected time the 
                    NETCONF client will wait before re-establishing
                    a connection to the NETCONF server.  The NETCONF
                    client may initiate a connection before this 
                    time if desired (e.g., to set configuration).";
                }
              }
            }
          }
        }
        container reconnect-strategy {
          description
           "The reconnection strategy directs how a NETCONF client 
            reconnects to a NETCONF server, after discovering its
            connection to the server has dropped, even if due to a
            reboot.  The NETCONF client starts with the specified
            endpoint and tries to connect to it max-attempts times
            before trying the next endpoint in the list (round 
            robin).";
          leaf start-with {
            type enumeration {
              enum first-listed {
                description
                  "Indicates that reconnections should start with
                   the first endpoint listed.";
              }
              enum last-connected { 
                description
                  "Indicates that reconnections should start with
                   the endpoint last connected to.  If no previous
                   connection has ever been established, then the
                   first endpoint configured is used.   NETCONF 
                   clients SHOULD be able to remember the last 
                   endpoint connected to across reboots.";
              }
            }
            default first-listed;
            description
             "Specifies which of the NETCONF server's endpoints the
              NETCONF client should start with when trying to connect
              to the NETCONF server.";
          }
          leaf max-attempts {
            type uint8 {
              range "1..max";
            }
            default 3;
            description
             "Specifies the number times the NETCONF client tries to
              connect to a specific endpoint before moving on to the
              next endpoint in the list (round robin).";
          }
        }
      } // end netconf-server
    } // end initiate

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

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

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

      list endpoint {
        key name;
        description
          "List of endpoints to listen for NETCONF connections.";
        leaf name {
          type string;
          description
            "An arbitrary name for the NETCONF listen endpoint.";
        }
        choice transport {
          mandatory true;
          description
            "Selects between available transports.";
          case ssh {
            if-feature ssh-listen;
            container ssh {
              description
                "SSH-specific listening configuration for inbound
                 connections.";
              leaf address {
                type inet:ip-address;
                description
                 "The IP address to listen for call-home connections.";
              }   
              leaf port {
                type inet:port-number;
                default 4334;
                description
                 "The port number to listen for call-home connections.";
              }   
              uses ss:ssh-client-grouping;
            }
          }
          case tls {
            if-feature tls-listen;
            container tls {
              description
                "TLS-specific listening configuration for inbound
                 connections.";
              leaf address {
                type inet:ip-address;
                description
                 "The IP address to listen for call-home connections.";
              }   
              leaf port {
                type inet:port-number;
                default 4335;
                description
                 "The port number to listen for call-home connections.";
              }   
              uses ts:tls-client-grouping {
                refine "client-auth" {
                  must 'certificate';
                  description
                    "NETCONF/TLS clients MUST pass a client certiticate.";
                }
              }
            }
          }
        } // end transport
      } // end endpoint
    } // end listen

  } // end netconf-client


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

<CODE ENDS>

3. The NETCONF Server Model

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

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

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

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

3.1. Tree Diagram

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

module: ietf-netconf-server
    +--rw netconf-server
       +--rw session-options
       |  +--rw hello-timeout?   uint16
       +--rw listen {listen}?
       |  +--rw max-sessions?   uint16
       |  +--rw idle-timeout?   uint16
       |  +--rw endpoint* [name]
       |     +--rw name    string
       |     +--rw (transport)
       |        +--:(ssh) {ssh-listen}?
       |        |  +--rw ssh
       |        |     +--rw address?            inet:ip-address
       |        |     +--rw port?               inet:port-number
       |        |     +--rw host-keys
       |        |     |  +--rw host-key* [name]
       |        |     |     +--rw name           string
       |        |     |     +--rw (host-key-type)
       |        |     |        +--:(public-key)
       |        |     |        |  +--rw public-key?
       |        |     |        |          -> /ks:keystore/keys/key/name
       |        |     |        +--:(certificate)
       |        |     |           +--rw certificate?   leafref
       |        |     |                   {sshcom:ssh-x509-certs}?
       |        |     +--rw client-cert-auth {sshcom:ssh-x509-certs}?
       |        |     |  +--rw trusted-ca-certs?       leafref
       |        |     |  +--rw trusted-client-certs?   leafref
       |        |     +--rw transport-params
       |        |             {ssh-server-transport-params-config}?
       |        |        +--rw host-key
       |        |        |  +--rw host-key-alg*   identityref
       |        |        +--rw key-exchange
       |        |        |  +--rw key-exchange-alg*   identityref
       |        |        +--rw encryption
       |        |        |  +--rw encryption-alg*   identityref
       |        |        +--rw mac
       |        |        |  +--rw mac-alg*   identityref
       |        |        +--rw compression
       |        |           +--rw compression-alg*   identityref
       |        +--:(tls) {tls-listen}?
       |           +--rw tls
       |              +--rw address?        inet:ip-address
       |              +--rw port?           inet:port-number
       |              +--rw certificates
       |              |  +--rw certificate* [name]
       |              |     +--rw name    leafref
       |              +--rw client-auth
       |              |  +--rw trusted-ca-certs?       leafref
       |              |  +--rw trusted-client-certs?   leafref
       |              |  +--rw cert-maps
       |              |     +--rw cert-to-name* [id]
       |              |        +--rw id             uint32
       |              |        +--rw fingerprint    x509c2n:tls-fingerprint
       |              |        +--rw map-type       identityref
       |              |        +--rw name           string
       |              +--rw hello-params
       |                      {tls-server-hello-params-config}?
       |                 +--rw tls-versions
       |                 |  +--rw tls-version*   identityref
       |                 +--rw cipher-suites
       |                    +--rw cipher-suite*   identityref
       +--rw call-home {call-home}?
          +--rw netconf-client* [name]
             +--rw name                  string
             +--rw (transport)
             |  +--:(ssh) {ssh-call-home}?
             |  |  +--rw ssh
             |  |     +--rw endpoints
             |  |     |  +--rw endpoint* [name]
             |  |     |     +--rw name       string
             |  |     |     +--rw address    inet:host
             |  |     |     +--rw port?      inet:port-number
             |  |     +--rw host-keys
             |  |     |  +--rw host-key* [name]
             |  |     |     +--rw name           string
             |  |     |     +--rw (host-key-type)
             |  |     |        +--:(public-key)
             |  |     |        |  +--rw public-key?
             |  |     |        |          -> /ks:keystore/keys/key/name
             |  |     |        +--:(certificate)
             |  |     |           +--rw certificate?   leafref
             |  |     |                   {sshcom:ssh-x509-certs}?
             |  |     +--rw client-cert-auth {sshcom:ssh-x509-certs}?
             |  |     |  +--rw trusted-ca-certs?       leafref
             |  |     |  +--rw trusted-client-certs?   leafref
             |  |     +--rw transport-params
             |  |             {ssh-server-transport-params-config}?
             |  |        +--rw host-key
             |  |        |  +--rw host-key-alg*   identityref
             |  |        +--rw key-exchange
             |  |        |  +--rw key-exchange-alg*   identityref
             |  |        +--rw encryption
             |  |        |  +--rw encryption-alg*   identityref
             |  |        +--rw mac
             |  |        |  +--rw mac-alg*   identityref
             |  |        +--rw compression
             |  |           +--rw compression-alg*   identityref
             |  +--:(tls) {tls-call-home}?
             |     +--rw tls
             |        +--rw endpoints
             |        |  +--rw endpoint* [name]
             |        |     +--rw name       string
             |        |     +--rw address    inet:host
             |        |     +--rw port?      inet:port-number
             |        +--rw certificates
             |        |  +--rw certificate* [name]
             |        |     +--rw name    leafref
             |        +--rw client-auth
             |        |  +--rw trusted-ca-certs?       leafref
             |        |  +--rw trusted-client-certs?   leafref
             |        |  +--rw cert-maps
             |        |     +--rw cert-to-name* [id]
             |        |        +--rw id             uint32
             |        |        +--rw fingerprint    x509c2n:tls-fingerprint
             |        |        +--rw map-type       identityref
             |        |        +--rw name           string
             |        +--rw hello-params
             |                {tls-server-hello-params-config}?
             |           +--rw tls-versions
             |           |  +--rw tls-version*   identityref
             |           +--rw cipher-suites
             |              +--rw cipher-suite*   identityref
             +--rw connection-type
             |  +--rw (connection-type)?
             |     +--:(persistent-connection)
             |     |  +--rw persistent!
             |     |     +--rw idle-timeout?   uint32
             |     |     +--rw keep-alives
             |     |        +--rw max-wait?       uint16
             |     |        +--rw max-attempts?   uint8
             |     +--:(periodic-connection)
             |        +--rw periodic!
             |           +--rw idle-timeout?        uint16
             |           +--rw reconnect-timeout?   uint16
             +--rw reconnect-strategy
                +--rw start-with?     enumeration
                +--rw max-attempts?   uint8

3.2. Example Usage

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

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

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

  <!-- listening for SSH and TLS connections -->
  <listen>
    <endpoint> <!-- listening for SSH connections -->
      <name>netconf/ssh</name>
      <ssh>
        <address>11.22.33.44</address>
        <host-keys>
          <host-key>
            <name>public-key</name>
            <public-key>ex-rsa-key</public-key>
          </host-key>
          <host-key>
            <name>certificate</name>
            <certificate>builtin-idevid-cert</certificate>
          </host-key>
        </host-keys>
        <client-cert-auth>
          <trusted-ca-certs>deployment-specific-ca-certs</trusted-ca-certs>
          <trusted-client-certs>explicitly-trusted-client-certs</trusted-client-certs>
        </client-cert-auth>
      </ssh>
    </endpoint>
    <endpoint> <!-- listening for TLS sessions -->
      <name>netconf/tls</name>
      <tls>
        <address>11.22.33.44</address>
        <certificates>
          <certificate>
            <name>tls-ec-cert</name>
          </certificate>
        </certificates>
        <client-auth>
          <trusted-ca-certs>deployment-specific-ca-certs</trusted-ca-certs>
          <trusted-client-certs>explicitly-trusted-client-certs</trusted-client-certs>
          <cert-maps>
            <cert-to-name>
              <id>1</id>
              <fingerprint>11:0A:05:11:00</fingerprint>
              <map-type>x509c2n:san-any</map-type>
            </cert-to-name>
            <cert-to-name>
              <id>2</id>
              <fingerprint>B3:4F:A1:8C:54</fingerprint>
              <map-type>x509c2n:specified</map-type>
              <name>scooby-doo</name>
            </cert-to-name>
          </cert-maps>
        </client-auth>
      </tls>
    </endpoint>
  </listen>

  <!-- calling home to an SSH and TLS based NETCONF clients -->
  <call-home>
    <netconf-client> <!-- SSH-based client -->
      <name>config-mgr</name>
      <ssh>
        <endpoints>
          <endpoint>
            <name>east-data-center</name>
            <address>11.22.33.44</address>
          </endpoint>
          <endpoint>
            <name>west-data-center</name>
            <address>55.66.77.88</address>
          </endpoint>
        </endpoints>
        <host-keys>
          <host-key>
            <name>certificate</name>
            <certificate>builtin-idevid-cert</certificate>
          </host-key>
        </host-keys>
        <client-cert-auth>
          <trusted-ca-certs>deployment-specific-ca-certs</trusted-ca-certs>
          <trusted-client-certs>explicitly-trusted-client-certs</trusted-client-certs>
        </client-cert-auth>
      </ssh>
      <connection-type>
        <periodic>
          <idle-timeout>300</idle-timeout>
          <reconnect-timeout>60</reconnect-timeout>
        </periodic>
      </connection-type>
      <reconnect-strategy>
        <start-with>last-connected</start-with>
        <max-attempts>3</max-attempts>
      </reconnect-strategy>
    </netconf-client>
    <netconf-client> <!-- TLS-based client -->
      <name>event-correlator</name>
      <tls>
        <endpoints>
          <endpoint>
            <name>east-data-center</name>
            <address>22.33.44.55</address>
          </endpoint>
          <endpoint>
            <name>west-data-center</name>
            <address>33.44.55.66</address>
          </endpoint>
        </endpoints>
        <certificates>
          <certificate>
            <name>tls-ec-cert</name>
          </certificate>
        </certificates>
        <client-auth>
          <trusted-ca-certs>deployment-specific-ca-certs</trusted-ca-certs>
          <trusted-client-certs>explicitly-trusted-client-certs</trusted-client-certs>
          <cert-maps>
            <cert-to-name>
              <id>1</id>
              <fingerprint>11:0A:05:11:00</fingerprint>
              <map-type>x509c2n:san-any</map-type>
            </cert-to-name>
            <cert-to-name>
              <id>2</id>
              <fingerprint>B3:4F:A1:8C:54</fingerprint>
              <map-type>x509c2n:specified</map-type>
              <name>scooby-doo</name>
            </cert-to-name>
          </cert-maps>
        </client-auth>
      </tls>
      <connection-type>
        <persistent>
          <idle-timeout>300</idle-timeout>
          <keep-alives>
            <max-wait>30</max-wait>
            <max-attempts>3</max-attempts>
          </keep-alives>
        </persistent>
      </connection-type>
      <reconnect-strategy>
        <start-with>first-listed</start-with>
        <max-attempts>3</max-attempts>
      </reconnect-strategy>
    </netconf-client>
  </call-home>
</netconf-server>

3.3. YANG Model

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


<CODE BEGINS> file "ietf-netconf-server@2017-06-13.yang"

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

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

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

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

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

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

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

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

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


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

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

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

    This version of this YANG module is part of RFC XXXX; see
    the RFC itself for full legal notices.";

  revision "2017-06-13" {
    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";
  }

  // top-level container  (groupings below)
  container netconf-server {
    description
      "Top-level container for NETCONF server configuration.";

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

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


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

    container call-home {
      if-feature call-home;
      description
        "Configures call-home behavior";
      list netconf-client {
        key name;
        description
          "List of NETCONF clients the NETCONF server is to initiate
           call-home connections to.";
        leaf name {
          type string;
          description
            "An arbitrary name for the remote NETCONF client.";
        }
        choice transport {
          mandatory true;
          description
            "Selects between available transports.";
          case ssh {
            if-feature ssh-call-home;
            container ssh {
              description
                "Specifies SSH-specific call-home transport
                 configuration.";
              uses endpoints-container {
                refine endpoints/endpoint/port {
                  default 4334;
                }
              }
              uses ss:ssh-server-grouping;
            }
          }
          case tls {
            if-feature tls-call-home;
            container tls {
              description
                "Specifies TLS-specific call-home transport
                 configuration.";
              uses endpoints-container {
                refine endpoints/endpoint/port {
                  default 4335;
                }
              }
              uses ts:tls-server-grouping {
                augment "client-auth" {
                  description
                    "Augments in the cert-to-name structure.";
                  uses cert-maps-grouping;
                }
              }
            }
          }
        }
        container connection-type {
          description
           "Indicates the kind of connection to use.";
          choice connection-type {
            description
              "Selects between available connection types.";
            case persistent-connection {
              container persistent {
                presence true;
                description
                 "Maintain a persistent connection to the NETCONF 
                  client. If the connection goes down, immediately 
                  start trying to reconnect to it, using the 
                  reconnection strategy.
    
                  This connection type minimizes any NETCONF client
                  to NETCONF server data-transfer delay, albeit at 
                  the expense of holding resources longer.";
                leaf idle-timeout {
                  type uint32;
                  units "seconds";
                  default 86400;  // one day;
                  description
                    "Specifies the maximum number of seconds that a 
                     a NETCONF session may remain idle. A NETCONF 
                     session will be dropped if it is idle for an 
                     interval longer than this number of seconds.  
                     If set to zero, then the server will never drop
                     a session because it is idle.  Sessions that 
                     have a notification subscription active are 
                     never dropped.";
                }
                container keep-alives {
                  description
                    "Configures the keep-alive policy, to proactively
                     test the aliveness of the SSH/TLS client.  An
                     unresponsive SSH/TLS client will be dropped after
                     approximately max-attempts * max-wait seconds.";
                  reference
                    "RFC 8071: NETCONF Call Home and RESTCONF Call
                     Home, Section 3.1, item S6";
                  leaf max-wait {
                    type uint16 {
                      range "1..max";
                    }
                    units seconds;
                    default 30;
                    description
                     "Sets the amount of time in seconds after which 
                      if no data has been received from the SSH/TLS
                      client, a SSH/TLS-level message will be sent 
                      to test the aliveness of the SSH/TLS client.";
                  }
                  leaf max-attempts {
                    type uint8;
                    default 3;
                    description
                     "Sets the maximum number of sequential keep-alive
                      messages that can fail to obtain a response from
                      the SSH/TLS client before assuming the SSH/TLS
                      client is no longer alive.";
                  }
                }
              }
            }
            case periodic-connection {
              container periodic {
                presence true;
                description
                 "Periodically connect to the NETCONF client, so that
                  the NETCONF client may deliver messages pending for
                  the NETCONF server.  The NETCONF client must close
                  the connection when it is ready to release it. Once
                  the connection has been closed, the NETCONF server
                  will restart its timer until the next connection.";
                leaf idle-timeout {
                  type uint16;
                  units "seconds";
                  default 300; // five minutes
                  description
                    "Specifies the maximum number of seconds that a 
                     a NETCONF session may remain idle. A NETCONF 
                     session will be dropped if it is idle for an 
                     interval longer than this number of seconds.  
                     If set to zero, then the server will never drop
                     a session because it is idle.  Sessions that 
                     have a notification subscription active are 
                     never dropped.";
                }
                leaf reconnect-timeout {
                  type uint16 {
                    range "1..max";
                  }
                  units minutes;
                  default 60;
                  description
                   "Sets the maximum amount of unconnected time the 
                    NETCONF server will wait before re-establishing
                    a connection to the NETCONF client.  The NETCONF
                    server may initiate a connection before this 
                    time if desired (e.g., to deliver an event
                    notification message).";
                }
              }
            }
          }
        }
        container reconnect-strategy {
          description
           "The reconnection strategy directs how a NETCONF server 
            reconnects to a NETCONF client, after discovering its
            connection to the client has dropped, even if due to a
            reboot.  The NETCONF server starts with the specified
            endpoint and tries to connect to it max-attempts times
            before trying the next endpoint in the list (round 
            robin).";
          leaf start-with {
            type enumeration {
              enum first-listed {
                description
                  "Indicates that reconnections should start with
                   the first endpoint listed.";
              }
              enum last-connected { 
                description
                  "Indicates that reconnections should start with
                   the endpoint last connected to.  If no previous
                   connection has ever been established, then the
                   first endpoint configured is used.   NETCONF 
                   servers SHOULD be able to remember the last 
                   endpoint connected to across reboots.";
              }
            }
            default first-listed;
            description
             "Specifies which of the NETCONF client's endpoints the
              NETCONF server should start with when trying to connect
              to the NETCONF client.";
          }
          leaf max-attempts {
            type uint8 {
              range "1..max";
            }
            default 3;
            description
             "Specifies the number times the NETCONF server tries to
              connect to a specific endpoint before moving on to the
              next endpoint in the list (round robin).";
          }
        }
      }
    }
  }


  grouping cert-maps-grouping {
    description
      "A grouping that defines a container around the
       cert-to-name structure defined in RFC 7407.";
    container cert-maps {
      uses x509c2n:cert-to-name;
      description
       "The cert-maps container is used by a TLS-based NETCONF
        server to map the NETCONF client's presented X.509
        certificate to a NETCONF username.  If no matching and
        valid cert-to-name list entry can be found, then the
        NETCONF server MUST close the connection, and MUST NOT
        accept NETCONF messages over it.";
      reference
        "RFC WWWW: NETCONF over TLS, Section 7";
    }
  }

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

}


<CODE ENDS>

4. Design Considerations

Editorial: this section is a hold over from before, previously called "Objectives". It was only written two support the "server" (not the "client"). The question is if it's better to add the missing "client" parts, or remove this section altogether.

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

4.1. Support all NETCONF transports

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

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

4.2. Enable each transport to select which keys to use

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

4.3. Support authenticating NETCONF clients certificates

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

4.4. Support mapping authenticated NETCONF client certificates to usernames

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

4.5. Support both listening for connections and call home

The NETCONF protocols were originally defined as having the server opening a port to listen for client connections. More recently the NETCONF working group defined support for call-home ([RFC8071]), enabling the server to initiate the connection to the client. Thus the modules defined herein should enable configuration for both listening for connections and calling home. Because implementations may not support both listening for connections and calling home, YANG "feature" statements should be used so that implementation can accurately advertise the connection types it supports.

4.6. For Call Home connections

The following objectives only pertain to call home connections.

4.6.1. Support more than one NETCONF client

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

4.6.2. Support NETCONF clients having more than one endpoint

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

4.6.3. Support a reconnection strategy

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

4.6.4. Support both persistent and periodic connections

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

4.6.5. Reconnection strategy for periodic connections

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

4.6.6. Keep-alives for persistent connections

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

4.6.7. Customizations for periodic connections

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

5. Security Considerations

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

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

The YANG module defined in this document is designed to be accessed via YANG based management protocols, such as NETCONF [RFC6241] and RESTCONF [RFC8040]. Both of these protocols have mandatory-to-implement secure transport layers (e.g., SSH, TLS) with mutual authentication.

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

There are a number of data nodes defined in this YANG module that are writable/creatable/deletable (i.e., config true, which is the default). These data nodes may be considered sensitive or vulnerable in some network environments. Write operations (e.g., edit-config) to these data nodes without proper protection can have a negative effect on network operations. These are the subtrees and data nodes and their sensitivity/vulnerability:

NONE

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

NONE

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

NONE

6. IANA Considerations

6.1. The IETF XML Registry

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

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

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

6.2. The YANG Module Names Registry

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

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

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

7. Acknowledgements

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

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

8. References

8.1. Normative References

[I-D.ietf-netconf-keystore] Watsen, K., "Keystore Model", Internet-Draft draft-ietf-netconf-keystore-01, March 2017.
[I-D.ietf-netconf-ssh-client-server] Watsen, K. and G. Wu, "SSH Client and Server Models", Internet-Draft draft-ietf-netconf-ssh-client-server-02, March 2017.
[I-D.ietf-netconf-tls-client-server] Watsen, K. and G. Wu, "TLS Client and Server Models", Internet-Draft draft-ietf-netconf-tls-client-server-02, March 2017.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[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.

8.2. Informative References

[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004.
[RFC4252] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252, January 2006.
[RFC4253] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253, January 2006.
[RFC4254] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Connection Protocol", RFC 4254, DOI 10.17487/RFC4254, January 2006.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008.
[RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration Protocol (NETCONF) Access Control Model", RFC 6536, DOI 10.17487/RFC6536, March 2012.
[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.

Appendix A. Change Log

A.1. server-model-09 to 00

A.2. 00 to 01

A.3. 01 to 02

A.4. 02 to 03

Authors' Addresses

Kent Watsen Juniper Networks EMail: kwatsen@juniper.net
Gary Wu Cisco Networks EMail: garywu@cisco.com
Juergen Schoenwaelder Jacobs University Bremen EMail: j.schoenwaelder@jacobs-university.de