NETCONF Working Group K. Watsen
Internet-Draft Watsen Networks
Intended status: Standards Track March 9, 2019
Expires: September 10, 2019

RESTCONF Client and Server Models
draft-ietf-netconf-restconf-client-server-10

Abstract

This document defines two YANG modules, one module to configure a RESTCONF client and the other module to configure a RESTCONF server. Both modules support the TLS transport protocol with both standard RESTCONF and RESTCONF 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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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 RESTCONF client and the other module to configure a RESTCONF server [RFC8040]. Both modules support the TLS [RFC8446] transport protocol with both standard RESTCONF and RESTCONF Call Home connections [RFC8071].

1.1. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

2. The RESTCONF Client Model

The RESTCONF 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, like that presented in [I-D.ietf-netconf-netconf-client-server], is designed to support any number of possible transports. RESTCONF only supports the TLS transport currently, thus this model only supports the TLS transport.

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 RESTCONF client supports.

2.1. Tree Diagram

The following tree diagram [RFC8340] provides an overview of the data model for the "ietf-restconf-client" module. Just the container is displayed below, but there is also a reusable grouping called "restconf-client-grouping" that the container is using.

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

module: ietf-restconf-client
  +--rw restconf-client
     +--rw initiate! {initiate}?
     |  +--rw restconf-server* [name]
     |     +--rw name         string
     |     +--rw endpoints
     |        +--rw endpoint* [name]
     |           +--rw name                  string
     |           +--rw (transport)
     |           |  +--:(https) {https-initiate}?
     |           |     +--rw https
     |           |        +--rw remote-address          inet:host
     |           |        +--rw remote-port?
     |           |        |       inet:port-number
     |           |        +--rw local-address?          inet:ip-addr\
\ess
     |           |        +--rw local-port?
     |           |        |       inet:port-number
     |           |        +--rw tcp-keepalives {tcp-client-keepalive\
\s}?
     |           |        |  +--rw idle-time?        uint16
     |           |        |  +--rw max-probes?       uint16
     |           |        |  +--rw probe-interval?   uint16
     |           |        +--rw tls-client-identity
     |           |        |  +--rw (auth-type)
     |           |        |     +--:(certificate)
     |           |        |        +--rw certificate
     |           |        |           +--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 tls-server-auth
     |           |        |  +--rw pinned-ca-certs?
     |           |        |  |       ta:pinned-certificates-ref
     |           |        |  |       {ta:x509-certificates}?
     |           |        |  +--rw pinned-server-certs?
     |           |        |          ta:pinned-certificates-ref
     |           |        |          {ta:x509-certificates}?
     |           |        +--rw tls-hello-params
     |           |        |       {tls-client-hello-params-config}?
     |           |        |  +--rw tls-versions
     |           |        |  |  +--rw tls-version*   identityref
     |           |        |  +--rw cipher-suites
     |           |        |     +--rw cipher-suite*   identityref
     |           |        +--rw tls-keepalives {tls-client-keepalive\
\s}?
     |           |        |  +--rw max-wait?       uint16
     |           |        |  +--rw max-attempts?   uint8
     |           |        +--rw http-client-identity
     |           |        |  +--rw (auth-type)?
     |           |        |     +--:(basic)
     |           |        |     |  +--rw basic
     |           |        |     |     +--rw user-id?    string
     |           |        |     |     +--rw password?   string
     |           |        |     +--:(bearer)
     |           |        |     |  +--rw bearer
     |           |        |     |     +--rw token?   string
     |           |        |     +--:(digest)
     |           |        |     |  +--rw digest
     |           |        |     |     +--rw username?   string
     |           |        |     |     +--rw password?   string
     |           |        |     +--:(hoba)
     |           |        |     |  +--rw hoba
     |           |        |     +--:(mutual)
     |           |        |     |  +--rw mutual
     |           |        |     +--:(negotiate)
     |           |        |     |  +--rw negotiate
     |           |        |     +--:(oauth)
     |           |        |     |  +--rw oauth
     |           |        |     +--:(scram-sha-1)
     |           |        |     |  +--rw scram-sha-1
     |           |        |     +--:(scram-sha-256)
     |           |        |     |  +--rw scram-sha-256
     |           |        |     +--:(vapid)
     |           |        |        +--rw vapid
     |           |        +--rw http-keepalives
     |           |                {http-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)
              +--:(https) {https-listen}?
                 +--rw https
                    +--rw local-address           inet:ip-address
                    +--rw local-port?             inet:port-number
                    +--rw tcp-keepalives {tcp-server-keepalives}?
                    |  +--rw idle-time?        uint16
                    |  +--rw max-probes?       uint16
                    |  +--rw probe-interval?   uint16
                    +--rw tls-client-identity
                    |  +--rw (auth-type)
                    |     +--:(certificate)
                    |        +--rw certificate
                    |           +--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-supporte\
\d}?
                    |                 +--rw keystore-reference?
                    |                         ks:asymmetric-key-cert\
\ificate-ref
                    +--rw tls-server-auth
                    |  +--rw pinned-ca-certs?
                    |  |       ta:pinned-certificates-ref
                    |  |       {ta:x509-certificates}?
                    |  +--rw pinned-server-certs?
                    |          ta:pinned-certificates-ref
                    |          {ta:x509-certificates}?
                    +--rw tls-hello-params
                    |       {tls-client-hello-params-config}?
                    |  +--rw tls-versions
                    |  |  +--rw tls-version*   identityref
                    |  +--rw cipher-suites
                    |     +--rw cipher-suite*   identityref
                    +--rw tls-keepalives {tls-client-keepalives}?
                    |  +--rw max-wait?       uint16
                    |  +--rw max-attempts?   uint8
                    +--rw http-client-identity
                    |  +--rw (auth-type)?
                    |     +--:(basic)
                    |     |  +--rw basic
                    |     |     +--rw user-id?    string
                    |     |     +--rw password?   string
                    |     +--:(bearer)
                    |     |  +--rw bearer
                    |     |     +--rw token?   string
                    |     +--:(digest)
                    |     |  +--rw digest
                    |     |     +--rw username?   string
                    |     |     +--rw password?   string
                    |     +--:(hoba)
                    |     |  +--rw hoba
                    |     +--:(mutual)
                    |     |  +--rw mutual
                    |     +--:(negotiate)
                    |     |  +--rw negotiate
                    |     +--:(oauth)
                    |     |  +--rw oauth
                    |     +--:(scram-sha-1)
                    |     |  +--rw scram-sha-1
                    |     +--:(scram-sha-256)
                    |     |  +--rw scram-sha-256
                    |     +--:(vapid)
                    |        +--rw vapid
                    +--rw http-keepalives {http-client-keepalives}?
                       +--rw max-wait?       uint16
                       +--rw max-attempts?   uint8

2.2. Example Usage

The following example illustrates configuring a RESTCONF client to initiate connections, as well as listening for call-home connections.

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) ===========

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

  <!-- RESTCONF servers to initiate connections to -->
  <initiate>
    <restconf-server>
      <name>corp-fw1</name>
      <endpoints>
        <endpoint>
          <name>corp-fw1.example.com</name>
          <https>
            <remote-address>corp-fw1.example.com</remote-address>
            <tcp-keepalives>
              <idle-time>15</idle-time>
              <max-probes>3</max-probes>
              <probe-interval>30</probe-interval>
            </tcp-keepalives>
            <tls-client-identity>
              <certificate>
                <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>
              </certificate>
            </tls-client-identity>
            <tls-server-auth>
              <pinned-ca-certs>explicitly-trusted-server-ca-certs</p\
\inned-ca-certs>
              <pinned-server-certs>explicitly-trusted-server-certs</\
\pinned-server-certs>
            </tls-server-auth>
            <tls-keepalives>
              <max-wait>30</max-wait>
              <max-attempts>3</max-attempts>
            </tls-keepalives>
            <http-client-identity>
              <basic>
                <user-id>bob</user-id>
                <password>secret</password>
              </basic>
            </http-client-identity>
            <http-keepalives>
              <max-wait>30</max-wait>
              <max-attempts>3</max-attempts>
            </http-keepalives>
          </https>
          <connection-type>
            <persistent/>
          </connection-type>
        </endpoint>
        <endpoint>
          <name>corp-fw2.example.com</name>
          <https>
            <remote-address>corp-fw2.example.com</remote-address>
            <tcp-keepalives>
              <idle-time>15</idle-time>
              <max-probes>3</max-probes>
              <probe-interval>30</probe-interval>
            </tcp-keepalives>
            <tls-client-identity>
              <certificate>
                <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>
              </certificate>
            </tls-client-identity>
            <tls-server-auth>
              <pinned-ca-certs>explicitly-trusted-server-ca-certs</p\
\inned-ca-certs>
              <pinned-server-certs>explicitly-trusted-server-certs</\
\pinned-server-certs>
            </tls-server-auth>
            <tls-keepalives>
              <max-wait>30</max-wait>
              <max-attempts>3</max-attempts>
            </tls-keepalives>
            <http-client-identity>
              <basic>
                <user-id>bob</user-id>
                <password>secret</password>
              </basic>
            </http-client-identity>
            <http-keepalives>
              <max-wait>30</max-wait>
              <max-attempts>3</max-attempts>
            </http-keepalives>
          </https>
          <connection-type>
            <persistent/>
          </connection-type>
        </endpoint>
      </endpoints>
    </restconf-server>
  </initiate>

  <!-- endpoints to listen for RESTCONF Call Home connections on -->
  <listen>
    <endpoint>
      <name>Intranet-facing listener</name>
      <https>
        <local-address>11.22.33.44</local-address>
        <tls-client-identity>
          <certificate>
            <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>
          </certificate>
        </tls-client-identity>
        <tls-server-auth>
          <pinned-ca-certs>explicitly-trusted-server-ca-certs</pinne\
\d-ca-certs>
          <pinned-server-certs>explicitly-trusted-server-certs</pinn\
\ed-server-certs>
        </tls-server-auth>
      </https>
    </endpoint>
  </listen>
</restconf-client>

2.3. YANG Module

This YANG module has normative references to [RFC6991], [RFC8040], and [RFC8071], [I-D.kwatsen-netconf-tcp-client-server], [I-D.ietf-netconf-tls-client-server], and [I-D.kwatsen-netconf-http-client-server].

<CODE BEGINS> file "ietf-restconf-client@2019-03-09.yang"
module ietf-restconf-client {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-restconf-client";
  prefix rcc;

  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-tls-client {
    prefix tlsc;
    reference
      "RFC BBBB: YANG Groupings for TLS Clients and TLS Servers";
  }

  import ietf-http-client {
    prefix httpc;
    reference
      "RFC CCCC: YANG Groupings for HTTP Clients and HTTP Servers";
  }

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

  contact
    "WG Web:   <http://datatracker.ietf.org/wg/restconf/>
     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 RESTCONF clients.

     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.

     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
     (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 2019-03-09 {
    description
      "Initial version";
    reference
      "RFC XXXX: RESTCONF Client and Server Models";
  }

  // Features

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

  feature https-initiate {
    if-feature "initiate";
    description
      "The ‘https-initiate’ feature indicates that the RESTCONF
       client supports initiating HTTPS connections to RESTCONF
       servers. This feature exists as HTTPS might not be a
       mandatory to implement transport in the future.";
    reference
      "RFC 8040: RESTCONF Protocol";
  }

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

  feature https-listen {
    if-feature "listen";
    description
      "The ‘https-listen’ feature indicates that the RESTCONF client
       supports opening a port to listen for incoming RESTCONF
       server call-home connections.  This feature exists as not
       all RESTCONF clients may support RESTCONF call home.";
    reference
      "RFC 8071: NETCONF Call Home and RESTCONF Call Home";
  }

  // Groupings

  grouping restconf-client-grouping {
    description
      "Top-level grouping for RESTCONF client configuration.";
    container initiate {
      if-feature "initiate";
      presence "Enables client to initiate TCP connections";
      description
        "Configures client initiating underlying TCP connections.";
      list restconf-server {
        key "name";
        min-elements 1;
        description
          "List of RESTCONF servers the RESTCONF client is to
           initiate connections to in parallel.";
        leaf name {
          type string;
          description
            "An arbitrary name for the RESTCONF server.";
        }
        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
               RESTCONF client 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. This is a
                 'choice' statement so as to support additional
                 transport options to be augmented in.";
              case https {
                if-feature "https-initiate";
                container https {
                  description
                    "Specifies HTTPS-specific transport
                     configuration.";
                  uses tcpc:tcp-client-grouping {
                    refine "remote-port" {
                      default "443";
                      description
                        "The RESTCONF client will attempt to
                         connect to the IANA-assigned well-known
                         port value for 'https' (443) if no value
                         is specified.";
                    }
                  }
                  uses tlsc:tls-client-grouping {
                    refine "tls-client-identity/auth-type" {
                      mandatory true;
                      description
                        "RESTCONF clients MUST pass some
                         authentication credentials.";
                    }
                  }
                  uses httpc:http-client-grouping;
                }
              } // https
            } // transport
            container connection-type {
              description
                "Indicates the RESTCONF client's preference for how
                 the RESTCONF 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
                       RESTCONF server. If the connection goes down,
                       immediately start trying to reconnect to it,
                       using the reconnection strategy.  This
                       connection type minimizes any RESTCONF server
                       to RESTCONF client data-transfer delay, albeit
                       at the expense of holding resources longer.";
                  }
                }
                case periodic-connection {
                  container periodic {
                    presence "Indicates that a periodic connection is
                              to be maintained.";
                    description
                      "Periodically connect to the RESTCONF server.
                       The RESTCONF server should close the
                       underlying TCP connection upon completing
                       planned activities.

                       This connection type increases resource
                       utilization, albeit with increased delay in
                       RESTCONF server to RESTCONF 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 the underlying TCP session may remain
                         idle. A TCP session will be dropped if it
                         is idle for an interval longer than this
                         number of seconds If set to zero, then the
                         RESTCONF client will never drop a session
                         because it is idle.";
                    }
                  }
                } // periodic-connection
              } // connection-type
            } // connection-type
            container reconnect-strategy {
              description
                "The reconnection strategy directs how a RESTCONF
                 client reconnects to a RESTCONF server, after
                 discovering its connection to the server has
                 dropped, even if due to a reboot.  The RESTCONF
                 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.   RESTCONF 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 RESTCONF server's
                   endpoints the RESTCONF client should start
                   with when trying to connect to the RESTCONF
                   server.";
              }
              leaf max-attempts {
                type uint8 {
                  range "1..max";
                }
                default "3";
                description
                  "Specifies the number times the RESTCONF client
                   tries to connect to a specific endpoint before
                   moving on to the next endpoint in the list
                   (round robin).";
              }
            } // reconnect-strategy
          } // endpoint
        } // endpoints
      } // restconf-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 an
           underlying TCP session may remain idle. A TCP 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 RESTCONF connections.";
        leaf name {
          type string;
          description
            "An arbitrary name for the RESTCONF listen endpoint.";
        }
        choice transport {
          mandatory true;
          description
            "Selects between available transports. This is a
             'choice' statement so as to support additional
             transport options to be augmented in.";
          case https {
            if-feature "https-listen";
            container https {
              description
                "HTTPS-specific listening configuration for inbound
                 connections.";
              uses tcps:tcp-server-grouping {
                refine "local-port" {
                  default "4336";
                  description
                    "The RESTCONF client will listen on the IANA-
                     assigned well-known port for 'restconf-ch-tls'
                     (4336) if no value is specified.";
                }
              }
              uses tlsc:tls-client-grouping {
                refine "tls-client-identity/auth-type" {
                  mandatory true;
                  description
                    "RESTCONF clients MUST pass some authentication
                     credentials.";
                }
              }
              uses httpc:http-client-grouping;
            } 
          } // case https
        } // transport
      } // endpoint
    } // listen
  } // restconf-client

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

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

3. The RESTCONF Server Model

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

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 RESTCONF server supports.

3.1. Tree Diagram

The following tree diagram [RFC8340] provides an overview of the data model for the "ietf-restconf-server" module. Just the container is displayed below, but there is also a reusable grouping called "restconf-server-grouping" that the container is using.

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

module: ietf-restconf-server
  +--rw restconf-server
     +--rw listen! {listen}?
     |  +--rw endpoint* [name]
     |     +--rw name           string
     |     +--rw (transport)
     |        +--:(https) {https-listen}?
     |           +--rw https
     |              +--rw local-address          inet:ip-address
     |              +--rw local-port?            inet:port-number
     |              +--rw tcp-keepalives {tcp-server-keepalives}?
     |              |  +--rw idle-time?        uint16
     |              |  +--rw max-probes?       uint16
     |              |  +--rw probe-interval?   uint16
     |              +--rw tls-server-identity
     |              |  +--rw (local-or-keystore)
     |              |     +--:(local) {local-keys-supported}?
     |              |     |  +--rw local-definition
     |              |     |     +--rw algorithm?
     |              |     |     |       asymmetric-key-algorithm-ref
     |              |     |     +--rw public-key?               bina\
\ry
     |              |     |     +--rw private-key?              union
     |              |     |     +---x generate-hidden-key
     |              |     |     |  +---w input
     |              |     |     |     +---w algorithm
     |              |     |     |             asymmetric-key-algorit\
\hm-ref
     |              |     |     +---x install-hidden-key
     |              |     |     |  +---w input
     |              |     |     |     +---w algorithm
     |              |     |     |     |       asymmetric-key-algorit\
\hm-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-certificate-r\
\ef
     |              +--rw tls-client-auth
     |              |  +--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 tls-hello-params
     |              |       {tls-server-hello-params-config}?
     |              |  +--rw tls-versions
     |              |  |  +--rw tls-version*   identityref
     |              |  +--rw cipher-suites
     |              |     +--rw cipher-suite*   identityref
     |              +--rw tls-keepalives {tls-server-keepalives}?
     |              |  +--rw max-wait?       uint16
     |              |  +--rw max-attempts?   uint8
     |              +--rw http-keepalives {http-server-keepalives}?
     |                 +--rw max-wait?       uint16
     |                 +--rw max-attempts?   uint8
     +--rw call-home! {call-home}?
        +--rw restconf-client* [name]
           +--rw name                  string
           +--rw endpoints
           |  +--rw endpoint* [name]
           |     +--rw name           string
           |     +--rw (transport)
           |        +--:(https) {https-call-home}?
           |           +--rw https
           |              +--rw remote-address         inet:host
           |              +--rw remote-port?           inet:port-num\
\ber
           |              +--rw local-address?         inet:ip-addre\
\ss
           |              +--rw local-port?            inet:port-num\
\ber
           |              +--rw tcp-keepalives {tcp-client-keepalive\
\s}?
           |              |  +--rw idle-time?        uint16
           |              |  +--rw max-probes?       uint16
           |              |  +--rw probe-interval?   uint16
           |              +--rw tls-server-identity
           |              |  +--rw (local-or-keystore)
           |              |     +--:(local) {local-keys-supported}?
           |              |     |  +--rw local-definition
           |              |     |     +--rw algorithm?
           |              |     |     |       asymmetric-key-algorit\
\hm-ref
           |              |     |     +--rw public-key?
           |              |     |     |       binary
           |              |     |     +--rw private-key?
           |              |     |     |       union
           |              |     |     +---x generate-hidden-key
           |              |     |     |  +---w input
           |              |     |     |     +---w algorithm
           |              |     |     |             asymmetric-key-a\
\lgorithm-ref
           |              |     |     +---x install-hidden-key
           |              |     |     |  +---w input
           |              |     |     |     +---w algorithm
           |              |     |     |     |       asymmetric-key-a\
\lgorithm-ref
           |              |     |     |     +---w public-key?    bin\
\ary
           |              |     |     |     +---w private-key?   bin\
\ary
           |              |     |     +--rw cert?
           |              |     |     |       end-entity-cert-cms
           |              |     |     +---n certificate-expiration
           |              |     |        +-- expiration-date
           |              |     |                yang:date-and-time
           |              |     +--:(keystore) {keystore-supported}?
           |              |        +--rw keystore-reference?
           |              |                ks:asymmetric-key-certifi\
\cate-ref
           |              +--rw tls-client-auth
           |              |  +--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 tls-hello-params
           |              |       {tls-server-hello-params-config}?
           |              |  +--rw tls-versions
           |              |  |  +--rw tls-version*   identityref
           |              |  +--rw cipher-suites
           |              |     +--rw cipher-suite*   identityref
           |              +--rw tls-keepalives {tls-server-keepalive\
\s}?
           |              |  +--rw max-wait?       uint16
           |              |  +--rw max-attempts?   uint8
           |              +--rw http-keepalives
           |                      {http-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

3.2. Example Usage

The following example illustrates configuring a RESTCONF server to listen for RESTCONF client connections, as well as configuring call-home to one RESTCONF client.

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) ===========

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

  <!-- endpoints to listen for RESTCONF connections on -->
  <listen>
    <endpoint>
      <name>netconf/tls</name>
      <https>
        <local-address>11.22.33.44</local-address>
        <tls-server-identity>
          <local-definition>
            <algorithm xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-cr\
\ypto-types">ct:rsa2048</algorithm>
            <private-key>base64encodedvalue==</private-key>
            <public-key>base64encodedvalue==</public-key>
            <cert>base64encodedvalue==</cert>
          </local-definition>
        </tls-server-identity>
        <tls-client-auth>
          <pinned-ca-certs>explicitly-trusted-client-ca-certs</pinne\
\d-ca-certs>
          <pinned-client-certs>explicitly-trusted-client-certs</pinn\
\ed-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>
        </tls-client-auth>
      </https>
    </endpoint>
  </listen>

  <!-- call home to a RESTCONF client with two endpoints -->
  <call-home>
    <restconf-client>
      <name>config-manager</name>
      <endpoints>
        <endpoint>
          <name>east-data-center</name>
          <https>
            <remote-address>east.example.com</remote-address>
            <tls-server-identity>
              <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>
                <cert>base64encodedvalue==</cert>
              </local-definition>
            </tls-server-identity>
            <tls-client-auth>
              <pinned-ca-certs>explicitly-trusted-client-ca-certs</p\
\inned-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>
            </tls-client-auth>
          </https>
        </endpoint>
        <endpoint>
          <name>west-data-center</name>
          <https>
            <remote-address>west.example.com</remote-address>
            <tcp-keepalives>
              <idle-time>15</idle-time>
              <max-probes>3</max-probes>
              <probe-interval>30</probe-interval>
            </tcp-keepalives>
            <tls-server-identity>
              <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>
                <cert>base64encodedvalue==</cert>
              </local-definition>
            </tls-server-identity>
            <tls-client-auth>
              <pinned-ca-certs>explicitly-trusted-client-ca-certs</p\
\inned-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>
            </tls-client-auth>
            <http-keepalives>
              <max-wait>30</max-wait>
              <max-attempts>3</max-attempts>
            </http-keepalives>
          </https>
        </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>
    </restconf-client>
  </call-home>
</restconf-server>

3.3. YANG Module

This YANG module has normative references to [RFC6991], [RFC7407], [RFC8040], [RFC8071], [I-D.kwatsen-netconf-tcp-client-server], [I-D.ietf-netconf-tls-client-server], and [I-D.kwatsen-netconf-http-client-server].

<CODE BEGINS> file "ietf-restconf-server@2019-03-09.yang"
module ietf-restconf-server {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-restconf-server";
  prefix rcs;

  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-tls-server {
    prefix tlss;
    reference
      "RFC BBBB: YANG Groupings for TLS Clients and TLS Servers";
  }

  import ietf-http-server {
    prefix https;
    reference
      "RFC CCCC: YANG Groupings for HTTP Clients and HTTP 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 RESTCONF servers.

     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.

     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
     (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 2019-03-09 {
    description
      "Initial version";
    reference
      "RFC XXXX: RESTCONF Client and Server Models";
  }

  // Features

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

  feature https-listen {
    if-feature "listen";
    description
      "The 'https-listen' feature indicates that the RESTCONF server
       supports opening a port to listen for incoming RESTCONF
       client connections.  This feature exists as HTTPS might not
       be a mandatory to implement transport in the future.";
    reference
      "RFC 8040: RESTCONF Protocol";
  }

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

  feature https-call-home {
    if-feature "call-home";
    description
      "The 'https-call-home' feature indicates that the RESTCONF
       server supports initiating connections to RESTCONF clients.
       This feature exists as not all RESTCONF servers may
       support RESTCONF call home.";
    reference
      "RFC 8071: NETCONF Call Home and RESTCONF Call Home";
  }

  // Groupings

  grouping restconf-server-grouping {
    description
      "Top-level grouping for RESTCONF server configuration.";
    container listen {
      if-feature "listen";
      presence "Enables server to listen for TCP connections";
      description "Configures listen behavior";
      list endpoint {
        key "name";
        min-elements 1;
        description
          "List of endpoints to listen for RESTCONF connections.";
        leaf name {
          type string;
          description
            "An arbitrary name for the RESTCONF listen endpoint.";
        }
        choice transport {
          mandatory true;
          description
            "Selects between available transports. This is a
             'choice' statement so as to support additional
             transport options to be augmented in.";
          case https {
            if-feature "https-listen";
            container https {
              description
                "HTTPS-specific listening configuration for inbound
                 connections.";
              uses tcps:tcp-server-grouping {
                refine "local-port" {
                  default "443";
                  description
                    "The RESTCONF server will listen on the IANA-
                     assigned well-known port value for 'https'
                     (443) if no value is specified.";
                }
              }
              uses tlss:tls-server-grouping {
                refine "tls-client-auth" {
                  must 'pinned-ca-certs or pinned-client-certs';
                  description
                    "RESTCONF servers MUST be able to validate
                     clients.";
                }
                augment "tls-client-auth" {
                  description
                    "Augments in the cert-to-name structure,
                     so the RESTCONF server can map TLS-layer
                     client certificates to RESTCONF usernames.";
                  container cert-maps {
                    uses x509c2n:cert-to-name;
                    description
                      "The cert-maps container is used by a TLS-
                       based RESTCONF server to map the RESTCONF
                       client's presented X.509 certificate to
                       a RESTCONF username.  If no matching and
                       valid cert-to-name list entry can be found,
                       then the RESTCONF server MUST close the
                       connection, and MUST NOT accept RESTCONF
                       messages over it.";
                    reference
                      "RFC 7407: A YANG Data Model for SNMP
                                 Configuration.";
                  }
                }
              }
              uses https:http-server-grouping;
            } // https container
          } // tls case
        } // transport
      } // endpoint
    } // listen

    container call-home {
      if-feature "call-home";
      presence "Enables server to initiate TCP connections";
      description "Configures call-home behavior";
      list restconf-client {
        key "name";
        min-elements 1;
        description
          "List of RESTCONF clients the RESTCONF server is to
           initiate call-home connections to in parallel.";
        leaf name {
          type string;
          description
            "An arbitrary name for the remote RESTCONF client.";
        }
        container endpoints {
          description
            "Container for the list of endpoints.";
          list endpoint {
            key "name";
            min-elements 1;
            ordered-by user;
            description
              "User-ordered list of endpoints for this RESTCONF
               client.  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. This is a
                 'choice' statement so as to support additional
                 transport options to be augmented in.";
              case https {
                if-feature "https-call-home";
                container https {
                  description
                    "Specifies HTTPS-specific call-home transport
                     configuration.";
                  uses tcpc:tcp-client-grouping {
                    refine "remote-port" {
                      default "4336";
                      description
                        "The RESTCONF server will attempt to connect
                         to the IANA-assigned well-known port for
                         'restconf-ch-tls' (4336) if no value is
                         specified.";
                    }
                  }
                  uses tlss:tls-server-grouping {
                    refine "tls-client-auth" {
                      must 'pinned-ca-certs or pinned-client-certs';
                      description
                        "RESTCONF servers MUST be able to validate
                         clients.";
                    }
                    augment "tls-client-auth" {
                      description
                        "Augments in the cert-to-name structure,
                         so the RESTCONF server can map TLS-layer
                         client certificates to RESTCONF usernames.";
                      container cert-maps {
                        uses x509c2n:cert-to-name;
                        description
                          "The cert-maps container is used by a
                           TLS-based RESTCONF server to map the
                           RESTCONF client's presented X.509
                           certificate to a RESTCONF username. If
                           no matching and valid cert-to-name list
                           entry can be found, then the RESTCONF
                           server MUST close the connection, and
                           MUST NOT accept RESTCONF messages over
                           it.";
                        reference
                          "RFC 7407: A YANG Data Model for SNMP
                           Configuration.";
                      }
                    }
                  }
                  uses https:http-server-grouping;
                }
              }
            } // transport
          } // endpoint
        } // endpoints
        container connection-type {
          description
            "Indicates the RESTCONF server's preference for how the
             RESTCONF 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 RESTCONF
                   client. If the connection goes down, immediately
                   start trying to reconnect to it, using the
                   reconnection strategy.

                   This connection type minimizes any RESTCONF
                   client to RESTCONF server data-transfer delay,
                   albeit at the expense of holding resources
                   longer.";
              }
            }
            case periodic-connection {
              container periodic {
                presence "Indicates that a periodic connection is
                          to be maintained.";
                description
                  "Periodically connect to the RESTCONF client.  The
                   RESTCONF client should close the underlying TCP
                   connection upon completing planned activities.

                   This connection type increases resource
                   utilization, albeit with increased delay in
                   RESTCONF client to RESTCONF 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
                     the underlying TCP session may remain idle.
                     A TCP 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 reconnect-strategy {
          description
            "The reconnection strategy directs how a RESTCONF server
             reconnects to a RESTCONF client after discovering its
             connection to the client has dropped, even if due to a
             reboot.  The RESTCONF 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.   RESTCONF
                   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 RESTCONF client's endpoints
               the RESTCONF server should start with when trying
               to connect to the RESTCONF client.";
          }
          leaf max-attempts {
            type uint8 {
              range "1..max";
            }
            default "3";
            description
              "Specifies the number times the RESTCONF server tries
               to connect to a specific endpoint before moving on to
               the next endpoint in the list (round robin).";
          }
        }
      } // restconf-client
    } // call-home
  } // restconf-server-grouping

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

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

4. Security Considerations

The YANG module defined in this document uses a grouping defined in [I-D.ietf-netconf-tls-client-server]. Please see the Security Considerations section in that document for concerns related that grouping.

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) [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 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:

/:
The entire data trees defined by the modules defined in this draft are sensitive to write operations. For instance, the addition or removal of references to keys, certificates, trusted anchors, etc., can dramatically alter the implemented security policy. However, no NACM annotations are applied as the data SHOULD be editable by users other than a designated 'recovery session'.

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

5. IANA Considerations

5.1. 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-restconf-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-restconf-server
   Registrant Contact: The NETCONF WG of the IETF.
   XML: N/A, the requested URI is an XML namespace.

5.2. 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-restconf-client
   namespace:    urn:ietf:params:xml:ns:yang:ietf-restconf-client
   prefix:       ncc
   reference:    RFC XXXX

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

6. References

6.1. Normative References

[I-D.ietf-netconf-keystore] Watsen, K., "YANG Data Model for a Centralized Keystore Mechanism", Internet-Draft draft-ietf-netconf-keystore-07, October 2018.
[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-08, October 2018.
[I-D.kwatsen-netconf-http-client-server] Watsen, K., "YANG Groupings for HTTP Clients and HTTP Servers", Internet-Draft draft-kwatsen-netconf-http-client-server-00, 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.
[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.
[RFC7950] Bjorklund, M., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016.
[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.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.

6.2. Informative References

[I-D.ietf-netconf-netconf-client-server] Watsen, K., "NETCONF Client and Server Models", Internet-Draft draft-ietf-netconf-netconf-client-server-08, October 2018.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004.
[RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J. and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011.
[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.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018.

Appendix A. Change Log

A.1. 00 to 01

A.2. 01 to 02

A.3. 02 to 03

A.4. 03 to 04

A.5. 04 to 05

A.6. 05 to 06

A.7. 06 to 07

A.8. 07 to 08

A.9. 08 to 09

A.10. 09 to 10

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