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NETCONF Working Group                                          K. Watsen
Internet-Draft                                          Juniper Networks
Intended status: Standards Track                      September 20, 2018
Expires: March 24, 2019


                   RESTCONF Client and Server Models
              draft-ietf-netconf-restconf-client-server-07

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:

   o  I-D.ietf-netconf-keystore

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

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

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

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

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

   o  "2018-09-20" --> the publication date of this draft

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

   o  Appendix A.  Change Log



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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/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 24, 2019.

Copyright Notice

   Copyright (c) 2018 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  The RESTCONF Client Model . . . . . . . . . . . . . . . . . .   3
     2.1.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .   7
     2.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .   9
   3.  The RESTCONF Server Model . . . . . . . . . . . . . . . . . .  18
     3.1.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .  18
     3.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .  21
     3.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  24
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  34
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  35
     5.1.  The IETF XML Registry . . . . . . . . . . . . . . . . . .  35
     5.2.  The YANG Module Names Registry  . . . . . . . . . . . . .  35



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   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  36
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  36
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  37
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  38
     A.1.  00 to 01  . . . . . . . . . . . . . . . . . . . . . . . .  38
     A.2.  01 to 02  . . . . . . . . . . . . . . . . . . . . . . . .  38
     A.3.  02 to 03  . . . . . . . . . . . . . . . . . . . . . . . .  38
     A.4.  03 to 04  . . . . . . . . . . . . . . . . . . . . . . . .  38
     A.5.  04 to 05  . . . . . . . . . . . . . . . . . . . . . . . .  38
     A.6.  05 to 06  . . . . . . . . . . . . . . . . . . . . . . . .  39
     A.7.  06 to 07  . . . . . . . . . . . . . . . . . . . . . . . .  39
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  39
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  39

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.





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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 for formatting only]

   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)
        |           |  +--:(tls) {tls-initiate}?
        |           |     +--rw tls
        |           |        +--rw address            inet:host
        |           |        +--rw port?              inet:port-number
        |           |        +--rw client-identity
        |           |        |  +--rw (auth-type)
        |           |        |     +--:(certificate)
        |           |        |        +--rw certificate
        |           |        |           +--rw (local-or-keystore)
        |           |        |              +--:(local)
        |           |        |              |        {local-keys-suppor\
   ted}?
        |           |        |              |  +--rw algorithm?
        |           |        |              |  |       ct:key-algorithm\
   -ref
        |           |        |              |  +--rw public-key?
        |           |        |              |  |       binary
        |           |        |              |  +--rw private-key?
        |           |        |              |  |       union
        |           |        |              |  +---x generate-hidden-key
        |           |        |              |  |  +---w input
        |           |        |              |  |     +---w algorithm
        |           |        |              |  |             ct:key-alg\
   orithm-ref
        |           |        |              |  +---x install-hidden-key
        |           |        |              |  |  +---w input
        |           |        |              |  |     +---w algorithm
        |           |        |              |  |     |       ct:key-alg\
   orithm-ref



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        |           |        |              |  |     +---w public-key?
        |           |        |              |  |     |       binary
        |           |        |              |  |     +---w private-key?
        |           |        |              |  |             binary
        |           |        |              |  +--rw cert
        |           |        |              |  |       ct:end-entity-ce\
   rt-cms
        |           |        |              |  +---n certificate-expira\
   tion
        |           |        |              |     +-- expiration-date?
        |           |        |              |             yang:date-and\
   -time
        |           |        |              +--:(keystore)
        |           |        |                       {keystore-supporte\
   d}?
        |           |        |                 +--rw reference?
        |           |        |                         ks:asymmetric-ke\
   y-certificate-ref
        |           |        +--rw 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 hello-params
        |           |                {tls-client-hello-params-config}?
        |           |           +--rw tls-versions
        |           |           |  +--rw tls-version*   identityref
        |           |           +--rw cipher-suites
        |           |              +--rw cipher-suite*   identityref
        |           +--rw connection-type
        |           |  +--rw (connection-type)
        |           |     +--:(persistent-connection)
        |           |     |  +--rw persistent!
        |           |     |     +--rw keep-alives
        |           |     |        +--rw max-wait?       uint16
        |           |     |        +--rw max-attempts?   uint8
        |           |     +--:(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



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           +--rw endpoint* [name]
              +--rw name         string
              +--rw (transport)
                 +--:(tls) {tls-listen}?
                    +--rw tls
                       +--rw address?           inet:ip-address
                       +--rw port?              inet:port-number
                       +--rw client-identity
                       |  +--rw (auth-type)
                       |     +--:(certificate)
                       |        +--rw certificate
                       |           +--rw (local-or-keystore)
                       |              +--:(local) {local-keys-supported\
   }?
                       |              |  +--rw algorithm?
                       |              |  |       ct:key-algorithm-ref
                       |              |  +--rw public-key?
                       |              |  |       binary
                       |              |  +--rw private-key?
                       |              |  |       union
                       |              |  +---x generate-hidden-key
                       |              |  |  +---w input
                       |              |  |     +---w algorithm
                       |              |  |             ct:key-algorithm\
   -ref
                       |              |  +---x install-hidden-key
                       |              |  |  +---w input
                       |              |  |     +---w algorithm
                       |              |  |     |       ct:key-algorithm\
   -ref
                       |              |  |     +---w public-key?    bin\
   ary
                       |              |  |     +---w private-key?   bin\
   ary
                       |              |  +--rw cert
                       |              |  |       ct:end-entity-cert-cms
                       |              |  +---n certificate-expiration
                       |              |     +-- expiration-date?
                       |              |             yang:date-and-time
                       |              +--:(keystore) {keystore-supporte\
   d}?
                       |                 +--rw reference?
                       |                         ks:asymmetric-key-cert\
   ificate-ref
                       +--rw server-auth
                       |  +--rw pinned-ca-certs?
                       |  |       ta:pinned-certificates-ref
                       |  |       {ta:x509-certificates}?



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                       |  +--rw pinned-server-certs?
                       |          ta:pinned-certificates-ref
                       |          {ta:x509-certificates}?
                       +--rw hello-params
                               {tls-client-hello-params-config}?
                          +--rw tls-versions
                          |  +--rw tls-version*   identityref
                          +--rw cipher-suites
                             +--rw cipher-suite*   identityref

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 for formatting only]

   <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>
             <tls>
               <address>corp-fw1.example.com</address>
               <client-identity>
                 <certificate>
                   <algorithm xmlns:ct="urn:ietf:params:xml:ns:yang:iet\
   f-crypto-types">ct:secp521r1</algorithm>
                   <private-key>base64encodedvalue==</private-key>
                   <public-key>base64encodedvalue==</public-key>
                   <cert>base64encodedvalue==</cert>
                 </certificate>
               </client-identity>
               <server-auth>
                 <pinned-ca-certs>explicitly-trusted-server-ca-certs</p\
   inned-ca-certs>
                 <pinned-server-certs>explicitly-trusted-server-certs</\
   pinned-server-certs>
               </server-auth>



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             </tls>
             <connection-type>
               <persistent/>
             </connection-type>
           </endpoint>
           <endpoint>
             <name>corp-fw2.example.com</name>
             <tls>
               <address>corp-fw2.example.com</address>
               <client-identity>
                 <certificate>
                   <algorithm xmlns:ct="urn:ietf:params:xml:ns:yang:iet\
   f-crypto-types">ct:secp521r1</algorithm>
                   <private-key>base64encodedvalue==</private-key>
                   <public-key>base64encodedvalue==</public-key>
                   <cert>base64encodedvalue==</cert>
                 </certificate>
               </client-identity>
               <server-auth>
                 <pinned-ca-certs>explicitly-trusted-server-ca-certs</p\
   inned-ca-certs>
                 <pinned-server-certs>explicitly-trusted-server-certs</\
   pinned-server-certs>
               </server-auth>
             </tls>
             <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>
         <tls>
           <address>11.22.33.44</address>
           <client-identity>
             <certificate>
               <algorithm xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-cr\
   ypto-types">ct:secp521r1</algorithm>
               <private-key>base64encodedvalue==</private-key>
               <public-key>base64encodedvalue==</public-key>
               <cert>base64encodedvalue==</cert>
             </certificate>
           </client-identity>



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           <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>
           </server-auth>
         </tls>
       </endpoint>
     </listen>
   </restconf-client>

2.3.  YANG Module

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

   <CODE BEGINS> file "ietf-restconf-client@2018-09-20.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-inet-types {
       prefix inet;
       reference
         "RFC 6991: Common YANG Data Types";
     }

     import ietf-tls-client {
       prefix ts;
       revision-date 2018-09-20; // stable grouping definitions
       reference
         "RFC ZZZZ: YANG Groupings for TLS Clients and TLS Servers";
     }

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

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



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       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 RESTCONF clients.

       Copyright (c) 2017 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 "2018-09-20" {
       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., TLS, etc.).";
     }

     feature tls-initiate {
       if-feature initiate;
       description
        "The 'tls-initiate' feature indicates that the RESTCONF client
         supports initiating TLS connections to RESTCONF servers. This
         feature exists as TLS might not be a mandatory to implement
         transport in the future.";
       reference



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        "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.,
         TLS, etc.).";
     }

     feature tls-listen {
       if-feature listen;
       description
        "The 'tls-listen' feature indicates that the RESTCONF client
         supports opening a port to listen for incoming RESTCONF
         server call-home TLS connections.  This feature exists as
         TLS might not be a mandatory to implement transport in the
         future.";
       reference
        "RFC 8071: NETCONF Call Home and RESTCONF Call Home";
     }

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

     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.";



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           }
           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 tls {
                   if-feature tls-initiate;
                   container tls {
                     description
                       "Specifies TLS-specific transport
                        configuration.";
                     leaf address {
                       type inet:host;
                       mandatory true;
                       description
                        "The IP address or hostname of the endpoint.
                         If a domain name is configured, then the
                         DNS resolution should happen on each usage
                         attempt.  If the the DNS resolution results
                         in multiple IP addresses, the IP addresses
                         will be tried according to local preference
                         order until a connection has been established
                         or until all IP addresses have failed.";
                     }
                     leaf port {
                       type inet:port-number;
                       default 443;
                       description
                        "The IP port for this endpoint. The RESTCONF
                         client will use the IANA-assigned well-known



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                         port for 'https' (443) if no value is
                         specified.";
                     }
                     uses ts:tls-client-grouping {
                       refine "client-identity/auth-type" {
                         mandatory true;
                         description
                           "RESTCONF clients MUST pass some
                            authentication credentials.";
                       }
                     }
                   }
                 } // end tls
               } // end transport
               container connection-type {
                 description
                  "Indicates the kind of connection to use.";
                 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.";
                       container keep-alives {
                         description
                           "Configures the keep-alive policy, to
                            proactively test the aliveness of the TLS
                            server.  An unresponsive TLS server will
                            be dropped after approximately max-attempts
                            * max-wait seconds.";
                         leaf max-wait {
                           type uint16 {
                             range "1..max";
                           }
                           units seconds;
                           default 30;
                           description



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                            "Sets the amount of time in seconds after
                             which if no data has been received from
                             the TLS server, a TLS-level message will
                             be sent to test the aliveness of the 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 TLS server
                             before assuming the TLS server is no
                             longer alive.";
                         }
                       }
                     }
                   }
                   case periodic-connection {
                     container periodic {
                       presence
                        "Indicates that a periodic connection is to be
                         maintained.";
                       description
                        "Periodically connect to the NETCONF server.
                         The RESTCONF server should close the underlying
                         TLS 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})';
                         }



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                         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 TLS session may remain
                            idle. A TLS 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.";
                       }
                     }
                   } // end periodic-connection
                 } // end connection-type
               } // end 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



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                          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).";
                 }
               } // end reconnect-strategy
             } // end endpoint
           } // end endpoints
         } // end restconf-server
       } // end 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



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              underlying TLS session may remain idle. A TLS 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 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 on for incoming call-
                     home connections.  The RESTCONF client will
                     listen on all configured interfaces if no
                     value is specified.  INADDR_ANY (0.0.0.0) or
                     INADDR6_ANY (0:0:0:0:0:0:0:0 a.k.a. ::) MUST
                     be used when the server is to listen on all
                     IPv4 or IPv6 addresses, respectively.";
                 }
                 leaf port {
                   type inet:port-number;
                   default 4336;
                   description
                    "The port number to listen on for call-home
                     connections. The RESTCONF client will listen
                     on the IANA-assigned well-known port for



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                     'restconf-ch-tls' (4336) if no value is
                      specified.";
                 }
                 uses ts:tls-client-grouping {
                   refine "client-identity/auth-type" {
                     mandatory true;
                     description
                       "RESTCONF clients MUST pass some authentication
                        credentials.";
                   }
                 }
               }
             }
           } // end transport
         } // end endpoint
       } // end listen
     } // end restconf-client
   }
   <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 for formatting only]

   module: ietf-restconf-server
     +--rw restconf-server
        +--rw listen! {listen}?
        |  +--rw endpoint* [name]
        |     +--rw name         string
        |     +--rw (transport)



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        |        +--:(tls) {tls-listen}?
        |           +--rw tls
        |              +--rw address?           inet:ip-address
        |              +--rw port?              inet:port-number
        |              +--rw server-identity
        |              |  +--rw (local-or-keystore)
        |              |     +--:(local) {local-keys-supported}?
        |              |     |  +--rw algorithm?
        |              |     |  |       ct:key-algorithm-ref
        |              |     |  +--rw public-key?               binary
        |              |     |  +--rw private-key?              union
        |              |     |  +---x generate-hidden-key
        |              |     |  |  +---w input
        |              |     |  |     +---w algorithm
        |              |     |  |             ct:key-algorithm-ref
        |              |     |  +---x install-hidden-key
        |              |     |  |  +---w input
        |              |     |  |     +---w algorithm
        |              |     |  |     |       ct:key-algorithm-ref
        |              |     |  |     +---w public-key?    binary
        |              |     |  |     +---w private-key?   binary
        |              |     |  +--rw cert
        |              |     |  |       ct:end-entity-cert-cms
        |              |     |  +---n certificate-expiration
        |              |     |     +-- expiration-date?
        |              |     |             yang:date-and-time
        |              |     +--:(keystore) {keystore-supported}?
        |              |        +--rw reference?
        |              |                ks:asymmetric-key-certificate-r\
   ef
        |              +--rw 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 hello-params
        |                      {tls-server-hello-params-config}?
        |                 +--rw tls-versions
        |                 |  +--rw tls-version*   identityref



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        |                 +--rw cipher-suites
        |                    +--rw cipher-suite*   identityref
        +--rw call-home! {call-home}?
           +--rw restconf-client* [name]
              +--rw name                  string
              +--rw endpoints
              |  +--rw endpoint* [name]
              |     +--rw name         string
              |     +--rw (transport)
              |        +--:(tls) {tls-call-home}?
              |           +--rw tls
              |              +--rw address            inet:host
              |              +--rw port?              inet:port-number
              |              +--rw server-identity
              |              |  +--rw (local-or-keystore)
              |              |     +--:(local) {local-keys-supported}?
              |              |     |  +--rw algorithm?
              |              |     |  |       ct:key-algorithm-ref
              |              |     |  +--rw public-key?
              |              |     |  |       binary
              |              |     |  +--rw private-key?
              |              |     |  |       union
              |              |     |  +---x generate-hidden-key
              |              |     |  |  +---w input
              |              |     |  |     +---w algorithm
              |              |     |  |             ct:key-algorithm-ref
              |              |     |  +---x install-hidden-key
              |              |     |  |  +---w input
              |              |     |  |     +---w algorithm
              |              |     |  |     |       ct:key-algorithm-ref
              |              |     |  |     +---w public-key?    binary
              |              |     |  |     +---w private-key?   binary
              |              |     |  +--rw cert
              |              |     |  |       ct:end-entity-cert-cms
              |              |     |  +---n certificate-expiration
              |              |     |     +-- expiration-date?
              |              |     |             yang:date-and-time
              |              |     +--:(keystore) {keystore-supported}?
              |              |        +--rw reference?
              |              |                ks:asymmetric-key-certifi\
   cate-ref
              |              +--rw client-auth
              |              |  +--rw pinned-ca-certs?
              |              |  |       ta:pinned-certificates-ref
              |              |  |       {ta:x509-certificates}?
              |              |  +--rw pinned-client-certs?
              |              |  |       ta:pinned-certificates-ref
              |              |  |       {ta:x509-certificates}?



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              |              |  +--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 keep-alives
              |     |        +--rw max-wait?       uint16
              |     |        +--rw max-attempts?   uint8
              |     +--:(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 for formatting only]

   <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>



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         <name>netconf/tls</name>
         <tls>
           <address>11.22.33.44</address>
           <server-identity>
             <algorithm xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-cryp\
   to-types">ct:secp521r1</algorithm>
             <private-key>base64encodedvalue==</private-key>
             <public-key>base64encodedvalue==</public-key>
             <cert>base64encodedvalue==</cert>
           </server-identity>
           <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>
           </client-auth>
         </tls>
       </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>
             <tls>
               <address>22.33.44.55</address>
               <server-identity>
                 <algorithm xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-\
   crypto-types">ct:secp521r1</algorithm>
                 <private-key>base64encodedvalue==</private-key>
                 <public-key>base64encodedvalue==</public-key>
                 <cert>base64encodedvalue==</cert>



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               </server-identity>
               <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>
               </client-auth>
             </tls>
           </endpoint>
           <endpoint>
             <name>west-data-center</name>
             <tls>
               <address>33.44.55.66</address>
               <server-identity>
                 <algorithm xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-\
   crypto-types">ct:secp521r1</algorithm>
                 <private-key>base64encodedvalue==</private-key>
                 <public-key>base64encodedvalue==</public-key>
                 <cert>base64encodedvalue==</cert>
               </server-identity>
               <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>



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                     <name>scooby-doo</name>
                   </cert-to-name>
                 </cert-maps>
               </client-auth>
             </tls>
           </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], and [I-D.ietf-netconf-tls-client-server].

   <CODE BEGINS> file "ietf-restconf-server@2018-09-20.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-inet-types {
       prefix inet;
       reference
         "RFC 6991: Common YANG Data Types";
     }

     import ietf-x509-cert-to-name {
       prefix x509c2n;



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       reference
         "RFC 7407: A YANG Data Model for SNMP Configuration";
     }

     import ietf-tls-server {
       prefix ts;
       revision-date 2018-09-20; // stable grouping definitions
       reference
         "RFC ZZZZ: YANG Groupings for TLS Clients and TLS Servers";
     }

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

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

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

       Copyright (c) 2017 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 "2018-09-20" {
       description
        "Initial version";



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       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., TLS, etc.).";
     }

     feature tls-listen {
       if-feature listen;
       description
        "The 'tls-listen' feature indicates that the RESTCONF server
         supports opening a port to listen for incoming RESTCONF
         client connections.  This feature exists as TLS 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.,
         TLS, etc.).";
       reference
        "RFC 8071: NETCONF Call Home and RESTCONF Call Home";
     }

     feature tls-call-home {
       if-feature call-home;
       description
        "The 'tls-call-home' feature indicates that the RESTCONF
         server supports initiating connections to RESTCONF clients.
         This feature exists as TLS might not be a mandatory to
         implement transport in the future.";
       reference
        "RFC 8071: NETCONF Call Home and RESTCONF Call Home";
     }

     container restconf-server {
       uses restconf-server-grouping;



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       description
         "Top-level container for RESTCONF server configuration.";
     }

     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 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 on for incoming
                    connections.  The RESTCONF server will listen
                    on all configured interfaces if no value is
                    specified.  INADDR_ANY (0.0.0.0) or INADDR6_ANY
                    (0:0:0:0:0:0:0:0 a.k.a. ::) MUST be used when
                    the server is to listen on all IPv4 or IPv6
                    addresses, respectively.";
                 }
                 leaf port {
                   type inet:port-number;
                   default 443;



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                   description
                    "The local port number to listen on.  If no value
                     is specified, the IANA-assigned port value for
                     'https' (443) is used.";
                 }
                 uses ts:tls-server-grouping {
                   refine "client-auth" {
                     must 'pinned-ca-certs or pinned-client-certs';
                     description
                       "RESTCONF servers MUST be able to validate
                        clients.";
                   }
                   augment "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.";
                     }
                   }
                 }
               } // end tls container
             } // end tls case
           } // end transport
         } // end endpoint
       } // end 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



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             "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 tls {
                   if-feature tls-call-home;
                   container tls {
                     description
                       "Specifies TLS-specific call-home transport
                        configuration.";
                     leaf address {
                       type inet:host;
                       mandatory true;
                       description
                        "The IP address or hostname of the endpoint.
                         If a domain name is configured, then the
                         DNS resolution should happen on each usage
                         attempt.  If the DNS resolution results in
                         multiple IP addresses, the IP addresses will
                         be tried according to local preference order
                         until a connection has been established or
                         until all IP addresses have failed.";
                     }



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                     leaf port {
                       type inet:port-number;
                       default 4336;
                       description
                        "The IP port for this endpoint.  The RESTCONF
                         server will use the IANA-assigned well-known
                         port for 'restconf-ch-tls' (4336) if no value
                         is specified.";
                     }
                     uses ts:tls-server-grouping {
                       refine "client-auth" {
                        must 'pinned-ca-certs or pinned-client-certs';
                        description
                         "RESTCONF servers MUST be able to validate
                          clients.";
                       }
                       augment "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.";
                         }
                       }
                     }
                   }
                 }
               } // end transport
             } // end endpoint
           } // end endpoints
           container connection-type {
             description
              "Indicates the RESTCONF client's preference for how the
               RESTCONF server's connection is maintained.";



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             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.";
                   container keep-alives {
                     description
                       "Configures the keep-alive policy, to
                        proactively test the aliveness of the TLS
                        client.  An unresponsive TLS client will
                        be dropped after approximately (max-attempts
                        * max-wait) seconds.";
                     reference
                       "RFC 8071: NETCONF Call Home and RESTCONF
                                  Call Home, Section 4.1, item S7";
                     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 TLS client, a TLS-level message will
                         be sent to test the aliveness of the 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



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                         response from the TLS client before assuming
                         the TLS client is no longer alive.";
                     }
                   }
                 }
               }
               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 TLS
                     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



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                        the underlying TLS session may remain idle.
                        A TLS 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 {



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               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).";
             }
           }
         }
       }
     }
   }
   <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'.



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   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





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6.  References

6.1.  Normative References

   [I-D.ietf-netconf-keystore]
              Watsen, K., "YANG Data Model for a Centralized Keystore
              Mechanism", draft-ietf-netconf-keystore-06 (work in
              progress), September 2018.

   [I-D.ietf-netconf-tls-client-server]
              Watsen, K. and G. Wu, "YANG Groupings for TLS Clients and
              TLS Servers", draft-ietf-netconf-tls-client-server-06
              (work in progress), June 2018.

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

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

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

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

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

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

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

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




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6.2.  Informative References

   [I-D.ietf-netconf-netconf-client-server]
              Watsen, K. and G. Wu, "NETCONF Client and Server Models",
              draft-ietf-netconf-netconf-client-server-06 (work in
              progress), June 2018.

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

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

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.























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Appendix A.  Change Log

A.1.  00 to 01

   o  Renamed "keychain" to "keystore".

A.2.  01 to 02

   o  Filled in previously missing 'ietf-restconf-client' module.

   o  Updated the ietf-restconf-server module to accomodate new grouping
      'ietf-tls-server-grouping'.

A.3.  02 to 03

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

   o  Changed restconf-client??? to be a grouping (not a container).

A.4.  03 to 04

   o  Added RFC 8174 to Requirements Language Section.

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

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

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

   o  Now tree diagrams reference ietf-netmod-yang-tree-diagrams

   o  Updated examples to inline key and certificates (no longer a
      leafref to keystore)

A.5.  04 to 05

   o  Now tree diagrams reference ietf-netmod-yang-tree-diagrams

   o  Updated examples to inline key and certificates (no longer a
      leafref to keystore)







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A.6.  05 to 06

   o  Fixed change log missing section issue.

   o  Updated examples to match latest updates to the crypto-types,
      trust-anchors, and keystore drafts.

   o  Reduced line length of the YANG modules to fit within 69 columns.

A.7.  06 to 07

   o  removed "idle-timeout" from "persistent" connection config.

   o  Added "random-selection" for reconnection-strategy's "starts-with"
      enum.

   o  Replaced "connection-type" choice default (persistent) with
      "mandatory true".

   o  Reduced the periodic-connection's "idle-timeout" from 5 to 2
      minutes.

   o  Replaced reconnect-timeout with period/anchor-time combo.

Acknowledgements

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

Author's Address

   Kent Watsen
   Juniper Networks

   EMail: kwatsen@juniper.net













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