Internet Engineering Task Force (IETF)                        A. Bierman
Request for Comments: 7317                                     YumaWorks
Category: Standards Track                                   M. Bjorklund
ISSN: 2070-1721                                           Tail-f Systems
                                                             August 2014

A YANG Data Model for System Management

Abstract

   This document defines a YANG data model for the configuration and
   identification of some common system properties within a device
   containing a Network Configuration Protocol (NETCONF) server.  This
   document also includes data node definitions for system
   identification, time-of-day management, user management, DNS resolver
   configuration, and some protocol operations for system management.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7317.

Copyright Notice

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

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

   1. Introduction ....................................................2
      1.1. Terminology ................................................3
      1.2. Tree Diagrams ..............................................3
   2. Objectives ......................................................4
      2.1. System Identification ......................................4
      2.2. System Time Management .....................................4
      2.3. User Authentication ........................................4
      2.4. DNS Resolver ...............................................5
      2.5. System Control .............................................5
   3. System Data Model ...............................................5
      3.1. System Identification ......................................5
      3.2. System Time Management .....................................6
      3.3. DNS Resolver Model .........................................7
      3.4. RADIUS Client Model ........................................7
      3.5. User Authentication Model ..................................8
           3.5.1. SSH Public Key Authentication .......................8
           3.5.2. Local User Password Authentication ..................9
           3.5.3. RADIUS Password Authentication ......................9
      3.6. System Control .............................................9
   4. Relationship to the SNMPv2-MIB .................................10
   5. IANA Crypt Hash YANG Module ....................................10
   6. System YANG Module .............................................13
   7. IANA Considerations ............................................31
   8. Security Considerations ........................................31
   9. References .....................................................33
      9.1. Normative References ......................................33
      9.2. Informative References ....................................35

1. Introduction

   This document defines a YANG [RFC6020] data model for the
   configuration and identification of some common properties within a
   device containing a Network Configuration Protocol (NETCONF) server.

   Devices that are managed by NETCONF and perhaps other mechanisms have
   common properties that need to be configured and monitored in a
   standard way.

   The "ietf-system" YANG module defined in this document provides the
   following features:

   o  configuration and monitoring of system identification

   o  configuration and monitoring of system time-of-day

   o  configuration of user authentication

   o  configuration of local users

   o  configuration of the DNS resolver

   o  system control operations (shutdown, restart, setting time)

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].

   The following terms are defined in [RFC6241] and are not redefined
   here:

   o  client

   o  configuration data

   o  server

   o  state data

   The following terms are defined in [RFC6020] and are not redefined
   here:

   o  augment

   o  data model

1.2. Tree Diagrams

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

   o  Brackets "[" and "]" enclose list keys.

   o  Abbreviations before data node names: "rw" means configuration
      (read-write), and "ro" means state data (read-only).

   o  Symbols after data node names: "?" means an optional node, "!"
      means a presence container, and "*" denotes a list and leaf-list.

   o  Parentheses enclose choice and case nodes, and case nodes are also
      marked with a colon (":").

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

2. Objectives

2.1. System Identification

   There are many common properties used to identify devices, operating
   systems, software versions, etc. that need to be supported in the
   system data module.  These objects are defined as operational state
   data, and the information returned by the server is intended to be
   specific to the device vendor.

   Some user-configurable administrative strings are also provided, such
   as the system location and description.

2.2. System Time Management

   Management of the date and time used by the system needs to be
   supported.  The use of one or more NTP servers to automatically set
   the system date and time needs to be possible.  Utilization of the
   Time Zone Database [RFC6557] also needs to be supported.  It should
   be possible to configure the system to use NTP.

2.3. User Authentication

   The authentication mechanism needs to support password authentication
   over RADIUS in order to support deployment scenarios with centralized
   authentication servers.  Additionally, for scenarios when no
   centralized authentication server exists or for situations where the
   centralized authentication server cannot be reached from the device,
   local users need to be supported.

   Since the mandatory transport protocol for NETCONF is Secure Shell
   (SSH) [RFC6242], the authentication model needs to support SSH's
   "publickey" and "password" authentication methods [RFC4252].

   The model for authentication configuration should be flexible enough
   to support authentication methods defined by other standards
   documents or by vendors.  It should be possible to configure the
   system authentication properties.

2.4. DNS Resolver

   The configuration of the DNS resolver within the system containing
   the NETCONF server is required in order to control how domain names
   are resolved.

2.5. System Control

A few operations are needed to support common tasks such as
restarting the device or setting the system date and time.

3. System Data Model

3.1. System Identification

   The data model for system identification has the following structure:

      +--rw system
      |  +--rw contact?          string
      |  +--rw hostname?         inet:domain-name
      |  +--rw location?         string
      +--ro system-state
         +--ro platform
            +--ro os-name?       string
            +--ro os-release?    string
            +--ro os-version?    string
            +--ro machine?       string

3.2. System Time Management

   The data model for system time management has the following
   structure:

      +--rw system
      |  +--rw clock
      |  |  +--rw (timezone)?
      |  |     +--:(timezone-name)
      |  |     |  +--rw timezone-name?     timezone-name
      |  |     +--:(timezone-utc-offset)
      |  |        +--rw timezone-utc-offset?   int16
      |  +--rw ntp!
      |     +--rw enabled?   boolean
      |     +--rw server* [name]
      |        +--rw name                string
      |        +--rw (transport)
      |        |  +--:(udp)
      |        |     +--rw udp
      |        |        +--rw address    inet:host
      |        |        +--rw port?      inet:port-number
      |        +--rw association-type?   enumeration
      |        +--rw iburst?             boolean
      |        +--rw prefer?             boolean
      +--ro system-state
         +--ro clock
            +--ro current-datetime?      yang:date-and-time
            +--ro boot-datetime?         yang:date-and-time

   New "case" statements can be added in future revisions of this data
   model, or through augmentation by some other data model.

3.3. DNS Resolver Model

   The data model for configuration of the DNS resolver has the
   following structure:

      +--rw system
         +--rw dns-resolver
            +--rw search*    inet:domain-name
            +--rw server* [name]
            |  +--rw name    string
            |  +--rw (transport)
            |     +--:(udp-and-tcp)
            |        +--udp-and-tcp
            |           +--rw address    inet:ip-address
            |           +--rw port?      inet:port-number
            +--rw options
               +--rw timeout?    uint8
               +--rw attempts?   uint8

   New "case" statements can be added in future revisions of this data
   model, or through augmentation by some other data model.

3.4. RADIUS Client Model

   The data model for configuration of the RADIUS client has the
   following structure:

      +--rw system
         +--rw radius
            +--rw server* [name]
            |  +--rw name                   string
            |  +--rw (transport)
            |  |  +--:(udp)
            |  |     +--rw udp
            |  |        +--rw address                inet:host
            |  |        +--rw authentication-port?   inet:port-number
            |  |        +--rw shared-secret          string
            |  +--rw authentication-type?   identityref
            +--rw options
               +--rw timeout?    uint8
               +--rw attempts?   uint8

   New "case" statements can be added in future revisions of this data
   model, or through augmentation by some other data model.

3.5. User Authentication Model

   This document defines three authentication methods for use with
   NETCONF:

   o  publickey for local users over SSH

   o  password for local users over any secure transport

   o  password for RADIUS users over any secure transport

   Additional methods can be defined by other standards documents or by
   vendors.

   This document defines two optional YANG features: "local-users" and
   "radius-authentication", which the server advertises to indicate
   support for configuring local users on the device and support for
   using RADIUS for authentication, respectively.

   The authentication parameters defined in this document are primarily
   used to configure authentication of NETCONF users but MAY also be
   used by other interfaces, e.g., a command line interface or a web-
   based user interface.

   The data model for user authentication has the following structure:

      +--rw system
         +--rw authentication
            +--rw user-authentication-order*   identityref
            +--rw user* [name]
               +--rw name        string
               +--rw password?   ianach:crypt-hash
               +--rw authorized-key* [name]
                  +--rw name         string
                  +--rw algorithm    string
                  +--rw key-data     binary

3.5.1. SSH Public Key Authentication

   If the NETCONF server advertises the "local-users" feature,
   configuration of local users and their SSH public keys is supported
   in the /system/authentication/user list.

   Public key authentication is requested by the SSH client.  If the
   "local-users" feature is supported, then when a NETCONF client starts
   an SSH session towards the server using the "publickey"
   authentication "method name" [RFC4252], the SSH server looks up the

   user name given in the SSH authentication request in the
   /system/authentication/user list and verifies the key as described in
   [RFC4253].

3.5.2. Local User Password Authentication

   If the NETCONF server advertises the "local-users" feature,
   configuration of local users and their passwords is supported in the
   /system/authentication/user list.

   For NETCONF transport protocols that support password authentication,
   the leaf-list "user-authentication-order" is used to control whether
   or not local user password authentication should be used.

   In SSH, password authentication is requested by the client.  Other
   NETCONF transport protocols MAY also support password authentication.

   When local user password authentication is requested, the NETCONF
   transport looks up the user name provided by the client in the
   /system/authentication/user list and verifies the password.

3.5.3. RADIUS Password Authentication

   If the NETCONF server advertises the "radius-authentication" feature,
   the device supports user authentication using RADIUS.

   For NETCONF transport protocols that support password authentication,
   the leaf-list "user-authentication-order" is used to control whether
   or not RADIUS password authentication should be used.

   In SSH, password authentication is requested by the client.  Other
   NETCONF transport protocols MAY also support password authentication.

3.6. System Control

   The following operations are defined:

      set-current-datetime
      system-restart
      system-shutdown

   Two protocol operations are included to restart or shut down the
   system.  The 'system-restart' operation can be used to restart the
   entire system (not just the NETCONF server).  The 'system-shutdown'
   operation can be used to power off the entire system.

4. Relationship to the SNMPv2-MIB

   If a device implements the SNMPv2-MIB [RFC3418], there are two
   objects that MAY be mapped by the implementation.  See the YANG
   module definition in Section 6 for details.  The following table
   lists the YANG data nodes with corresponding objects in the
   SNMPv2-MIB.

                  +----------------+-------------------+
                  | YANG data node | SNMPv2-MIB object |
                  +----------------+-------------------+
                  | contact        | sysContact        |
                  | location       | sysLocation       |
                  +----------------+-------------------+

                YANG Interface Configuration Data Nodes and
                        Related SNMPv2-MIB Objects

5. IANA Crypt Hash YANG Module

   This YANG module references [RFC1321], [IEEE-1003.1-2008], and
   [FIPS.180-4.2012].

   <CODE BEGINS> file "iana-crypt-hash@2014-08-06.yang"

   module iana-crypt-hash {
     namespace "urn:ietf:params:xml:ns:yang:iana-crypt-hash";
     prefix ianach;

     organization "IANA";
     contact
       "        Internet Assigned Numbers Authority

        Postal: ICANN
                12025 Waterfront Drive, Suite 300
                Los Angeles, CA  90094-2536
                United States

        Tel:    +1 310 301 5800
        E-Mail: iana@iana.org>";
     description
       "This YANG module defines a type for storing passwords
        using a hash function and features to indicate which hash
        functions are supported by an implementation.

        The latest revision of this YANG module can be obtained from
        the IANA web site.

        Requests for new values should be made to IANA via
        email (iana@iana.org).

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

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

        The initial version of this YANG module is part of RFC 7317;
        see the RFC itself for full legal notices.";

     revision 2014-08-06 {
       description
         "Initial revision.";
       reference
         "RFC 7317: A YANG Data Model for System Management";
     }

     typedef crypt-hash {
       type string {
         pattern
           '$0$.*'
         + '|$1$[a-zA-Z0-9./]{1,8}$[a-zA-Z0-9./]{22}'
         + '|$5$(rounds=\d+$)?[a-zA-Z0-9./]{1,16}$[a-zA-Z0-9./]{43}'
         + '|$6$(rounds=\d+$)?[a-zA-Z0-9./]{1,16}$[a-zA-Z0-9./]{86}';
       }
       description
         "The crypt-hash type is used to store passwords using
          a hash function.  The algorithms for applying the hash
          function and encoding the result are implemented in
          various UNIX systems as the function crypt(3).

          A value of this type matches one of the forms:

            $0$<clear text password>
            $<id>$<salt>$<password hash>
            $<id>$<parameter>$<salt>$<password hash>

          The '$0$' prefix signals that the value is clear text.  When
          such a value is received by the server, a hash value is
          calculated, and the string '$<id>$<salt>$' or
          $<id>$<parameter>$<salt>$ is prepended to the result.  This
          value is stored in the configuration data store.

          If a value starting with '$<id>$', where <id> is not '0', is
          received, the server knows that the value already represents a
          hashed value and stores it 'as is' in the data store.

          When a server needs to verify a password given by a user, it
          finds the stored password hash string for that user, extracts
          the salt, and calculates the hash with the salt and given
          password as input.  If the calculated hash value is the same
          as the stored value, the password given by the client is
          accepted.

          This type defines the following hash functions:

            id | hash function | feature
            ---+---------------+-------------------
             1 | MD5           | crypt-hash-md5
             5 | SHA-256       | crypt-hash-sha-256
             6 | SHA-512       | crypt-hash-sha-512

          The server indicates support for the different hash functions
          by advertising the corresponding feature.";
       reference
         "IEEE Std 1003.1-2008 - crypt() function
          RFC 1321: The MD5 Message-Digest Algorithm
          FIPS.180-4.2012: Secure Hash Standard (SHS)";
     }

     feature crypt-hash-md5 {
       description
         "Indicates that the device supports the MD5
          hash function in 'crypt-hash' values.";
       reference "RFC 1321: The MD5 Message-Digest Algorithm";
     }

     feature crypt-hash-sha-256 {
       description
         "Indicates that the device supports the SHA-256
          hash function in 'crypt-hash' values.";
       reference "FIPS.180-4.2012: Secure Hash Standard (SHS)";
     }

     feature crypt-hash-sha-512 {
       description
         "Indicates that the device supports the SHA-512
          hash function in 'crypt-hash' values.";
       reference "FIPS.180-4.2012: Secure Hash Standard (SHS)";
     }

   }

   <CODE ENDS>

6. System YANG Module

   This YANG module imports YANG extensions from [RFC6536] and imports
   YANG types from [RFC6991].  It also references [RFC1035], [RFC2865],
   [RFC3418], [RFC5607], [RFC5966], and [RFC6557].

   <CODE BEGINS> file "ietf-system@2014-08-06.yang"

  module ietf-system {
    namespace "urn:ietf:params:xml:ns:yang:ietf-system";
    prefix "sys";

    import ietf-yang-types {
      prefix yang;
    }

    import ietf-inet-types {
      prefix inet;
    }

    import ietf-netconf-acm {
      prefix nacm;
    }

    import iana-crypt-hash {
      prefix ianach;
    }

    organization
      "IETF NETMOD (NETCONF Data Modeling Language) Working Group";

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

       WG Chair: Thomas Nadeau
                 <mailto:tnadeau@lucidvision.com>

       WG Chair: Juergen Schoenwaelder
                 <mailto:j.schoenwaelder@jacobs-university.de>

       Editor:   Andy Bierman
                 <mailto:andy@yumaworks.com>

       Editor:   Martin Bjorklund
                 <mailto:mbj@tail-f.com>";

    description
      "This module contains a collection of YANG definitions for the
       configuration and identification of some common system
       properties within a device containing a NETCONF server.  This
       includes data node definitions for system identification,
       time-of-day management, user management, DNS resolver
       configuration, and some protocol operations for system
       management.

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

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

       This version of this YANG module is part of RFC 7317; see
       the RFC itself for full legal notices.";

    revision 2014-08-06 {
      description
        "Initial revision.";
      reference
        "RFC 7317: A YANG Data Model for System Management";
    }

   /*
    * Typedefs
    */

    typedef timezone-name {
      type string;
      description
        "A time zone name as used by the Time Zone Database,
         sometimes referred to as the 'Olson Database'.

         The exact set of valid values is an implementation-specific
         matter.  Client discovery of the exact set of time zone names
         for a particular server is out of scope.";
      reference
        "RFC 6557: Procedures for Maintaining the Time Zone Database";
     }

    /*
     * Features
     */

    feature radius {
      description
        "Indicates that the device can be configured as a RADIUS
         client.";
      reference
        "RFC 2865: Remote Authentication Dial In User Service (RADIUS)";
    }

    feature authentication {
      description
        "Indicates that the device supports configuration of
         user authentication.";
    }

    feature local-users {
      if-feature authentication;
      description
        "Indicates that the device supports configuration of
         local user authentication.";
    }

    feature radius-authentication {
      if-feature radius;
      if-feature authentication;
      description
        "Indicates that the device supports configuration of user
         authentication over RADIUS.";
      reference
        "RFC 2865: Remote Authentication Dial In User Service (RADIUS)
         RFC 5607: Remote Authentication Dial-In User Service (RADIUS)
                   Authorization for Network Access Server (NAS)
                   Management";
    }

    feature ntp {
      description
        "Indicates that the device can be configured to use one or
         more NTP servers to set the system date and time.";
    }

    feature ntp-udp-port {
      if-feature ntp;
      description
        "Indicates that the device supports the configuration of
         the UDP port for NTP servers.

         This is a 'feature', since many implementations do not support
         any port other than the default port.";
    }

    feature timezone-name {
      description
        "Indicates that the local time zone on the device
         can be configured to use the TZ database
         to set the time zone and manage daylight saving time.";
      reference
        "RFC 6557: Procedures for Maintaining the Time Zone Database";
    }

    feature dns-udp-tcp-port {
      description
        "Indicates that the device supports the configuration of
         the UDP and TCP port for DNS servers.

         This is a 'feature', since many implementations do not support
         any port other than the default port.";
    }

    /*
     * Identities
     */

    identity authentication-method {
      description
        "Base identity for user authentication methods.";
    }

    identity radius {
      base authentication-method;
      description
        "Indicates user authentication using RADIUS.";
      reference
        "RFC 2865: Remote Authentication Dial In User Service (RADIUS)
         RFC 5607: Remote Authentication Dial-In User Service (RADIUS)
                   Authorization for Network Access Server (NAS)
                   Management";
    }

    identity local-users {
      base authentication-method;
      description
        "Indicates password-based authentication of locally
         configured users.";
    }

    identity radius-authentication-type {
      description
        "Base identity for RADIUS authentication types.";
    }

    identity radius-pap {
      base radius-authentication-type;
      description
        "The device requests Password Authentication Protocol (PAP)
         authentication from the RADIUS server.";
      reference
        "RFC 2865: Remote Authentication Dial In User Service (RADIUS)";
    }

    identity radius-chap {
      base radius-authentication-type;
      description
        "The device requests Challenge Handshake Authentication
         Protocol (CHAP) authentication from the RADIUS server.";
      reference
        "RFC 2865: Remote Authentication Dial In User Service (RADIUS)";
    }

    /*
     * Configuration data nodes
     */

    container system {
      description
        "System group configuration.";

      leaf contact {
        type string;
        description
          "The administrator contact information for the system.

           A server implementation MAY map this leaf to the sysContact
           MIB object.  Such an implementation needs to use some
           mechanism to handle the differences in size and characters
           allowed between this leaf and sysContact.  The definition of
           such a mechanism is outside the scope of this document.";
        reference
          "RFC 3418: Management Information Base (MIB) for the
                     Simple Network Management Protocol (SNMP)
                     SNMPv2-MIB.sysContact";
      }
      leaf hostname {
        type inet:domain-name;
       description
         "The name of the host.  This name can be a single domain
          label or the fully qualified domain name of the host.";
      }
      leaf location {
        type string;
        description
          "The system location.

           A server implementation MAY map this leaf to the sysLocation
           MIB object.  Such an implementation needs to use some
           mechanism to handle the differences in size and characters
           allowed between this leaf and sysLocation.  The definition
           of such a mechanism is outside the scope of this document.";

        reference
          "RFC 3418: Management Information Base (MIB) for the
                     Simple Network Management Protocol (SNMP)
                     SNMPv2-MIB.sysLocation";
      }

      container clock {
        description
          "Configuration of the system date and time properties.";

        choice timezone {
          description
            "The system time zone information.";

          case timezone-name {
            if-feature timezone-name;
            leaf timezone-name {
              type timezone-name;
              description
                "The TZ database name to use for the system, such
                 as 'Europe/Stockholm'.";
            }
          }
          case timezone-utc-offset {
            leaf timezone-utc-offset {
              type int16 {
                range "-1500 .. 1500";
              }
              units "minutes";
              description
                "The number of minutes to add to UTC time to
                 identify the time zone for this system.  For example,
                 'UTC - 8:00 hours' would be represented as '-480'.
                 Note that automatic daylight saving time adjustment
                 is not provided if this object is used.";
            }
          }
        }
      }

      container ntp {
        if-feature ntp;
        presence
          "Enables the NTP client unless the 'enabled' leaf
           (which defaults to 'true') is set to 'false'";
        description
          "Configuration of the NTP client.";

        leaf enabled {
          type boolean;
          default true;
          description
            "Indicates that the system should attempt to
             synchronize the system clock with an NTP server
             from the 'ntp/server' list.";
        }
        list server {
          key name;
          description
            "List of NTP servers to use for system clock
             synchronization.  If '/system/ntp/enabled'
             is 'true', then the system will attempt to
             contact and utilize the specified NTP servers.";

          leaf name {
            type string;
            description
              "An arbitrary name for the NTP server.";
          }
          choice transport {
            mandatory true;
            description
              "The transport-protocol-specific parameters for this
               server.";

            case udp {
              container udp {
                description
                  "Contains UDP-specific configuration parameters
                   for NTP.";
                leaf address {
                  type inet:host;
                  mandatory true;
                  description
                    "The address of the NTP server.";
                }
                leaf port {
                  if-feature ntp-udp-port;
                  type inet:port-number;
                  default 123;
                  description
                    "The port number of the NTP server.";
                }
              }
            }
          }

          leaf association-type {
            type enumeration {
              enum server {
                description
                  "Use client association mode.  This device
                   will not provide synchronization to the
                   configured NTP server.";
              }
              enum peer {
                description
                  "Use symmetric active association mode.
                   This device may provide synchronization
                   to the configured NTP server.";
              }
              enum pool {
                description
                  "Use client association mode with one or
                   more of the NTP servers found by DNS
                   resolution of the domain name given by
                   the 'address' leaf.  This device will not
                   provide synchronization to the servers.";
              }
            }
            default server;
            description
              "The desired association type for this NTP server.";
          }
          leaf iburst {
            type boolean;
            default false;
            description
              "Indicates whether this server should enable burst
               synchronization or not.";
          }
          leaf prefer {
            type boolean;
            default false;
            description
              "Indicates whether this server should be preferred
               or not.";
          }
        }
      }

      container dns-resolver {
        description
          "Configuration of the DNS resolver.";

        leaf-list search {
          type inet:domain-name;
          ordered-by user;
          description
            "An ordered list of domains to search when resolving
             a host name.";
        }
        list server {
          key name;
          ordered-by user;
          description
            "List of the DNS servers that the resolver should query.

             When the resolver is invoked by a calling application, it
             sends the query to the first name server in this list.  If
             no response has been received within 'timeout' seconds,
             the resolver continues with the next server in the list.
             If no response is received from any server, the resolver
             continues with the first server again.  When the resolver
             has traversed the list 'attempts' times without receiving
             any response, it gives up and returns an error to the
             calling application.

             Implementations MAY limit the number of entries in this
             list.";

          leaf name {
            type string;
            description
              "An arbitrary name for the DNS server.";
          }
          choice transport {
            mandatory true;
            description
              "The transport-protocol-specific parameters for this
               server.";

            case udp-and-tcp {
              container udp-and-tcp {
                description
                  "Contains UDP- and TCP-specific configuration
                   parameters for DNS.";
                reference
                  "RFC 1035: Domain Names - Implementation and
                             Specification
                   RFC 5966: DNS Transport over TCP - Implementation
                             Requirements";

                leaf address {
                  type inet:ip-address;
                  mandatory true;
                  description
                    "The address of the DNS server.";
                }
                leaf port {
                  if-feature dns-udp-tcp-port;
                  type inet:port-number;
                  default 53;
                  description
                    "The UDP and TCP port number of the DNS server.";
                }
              }
            }
          }
        }
        container options {
          description
            "Resolver options.  The set of available options has been
             limited to those that are generally available across
             different resolver implementations and generally useful.";
          leaf timeout {
            type uint8 {
              range "1..max";
            }
            units "seconds";
            default "5";
            description
              "The amount of time the resolver will wait for a
               response from each remote name server before
               retrying the query via a different name server.";
          }
          leaf attempts {
            type uint8 {
              range "1..max";
            }
            default "2";
            description
              "The number of times the resolver will send a query to
               all of its name servers before giving up and returning
               an error to the calling application.";
          }
        }
      }

      container radius {
        if-feature radius;

        description
          "Configuration of the RADIUS client.";

        list server {
          key name;
          ordered-by user;
          description
            "List of RADIUS servers used by the device.

             When the RADIUS client is invoked by a calling
             application, it sends the query to the first server in
             this list.  If no response has been received within
             'timeout' seconds, the client continues with the next
             server in the list.  If no response is received from any
             server, the client continues with the first server again.
             When the client has traversed the list 'attempts' times
             without receiving any response, it gives up and returns an
             error to the calling application.";

          leaf name {
            type string;
            description
              "An arbitrary name for the RADIUS server.";
          }
          choice transport {
            mandatory true;
            description
              "The transport-protocol-specific parameters for this
               server.";

            case udp {
              container udp {
                description
                  "Contains UDP-specific configuration parameters
                   for RADIUS.";
                leaf address {
                  type inet:host;
                  mandatory true;
                  description
                    "The address of the RADIUS server.";
                }

                leaf authentication-port {
                  type inet:port-number;
                  default "1812";
                  description
                    "The port number of the RADIUS server.";
                }
                leaf shared-secret {
                  type string;
                  mandatory true;
                  nacm:default-deny-all;
                  description
                    "The shared secret, which is known to both the
                     RADIUS client and server.";
                  reference
                    "RFC 2865: Remote Authentication Dial In User
                               Service (RADIUS)";
                }
              }
            }
          }
          leaf authentication-type {
            type identityref {
              base radius-authentication-type;
            }
            default radius-pap;
            description
              "The authentication type requested from the RADIUS
               server.";
          }
        }
        container options {
          description
            "RADIUS client options.";

          leaf timeout {
            type uint8 {
              range "1..max";
            }
            units "seconds";
            default "5";
            description
              "The number of seconds the device will wait for a
               response from each RADIUS server before trying with a
               different server.";
          }

          leaf attempts {
            type uint8 {
              range "1..max";
            }
            default "2";
            description
              "The number of times the device will send a query to
               all of its RADIUS servers before giving up.";
          }
        }
      }

      container authentication {
        nacm:default-deny-write;
        if-feature authentication;

         description
           "The authentication configuration subtree.";

         leaf-list user-authentication-order {
           type identityref {
             base authentication-method;
           }
           must '(. != "sys:radius" or ../../radius/server)' {
             error-message
               "When 'radius' is used, a RADIUS server"
             + " must be configured.";
             description
               "When 'radius' is used as an authentication method,
                a RADIUS server must be configured.";
           }
           ordered-by user;

           description
             "When the device authenticates a user with a password,
              it tries the authentication methods in this leaf-list in
              order.  If authentication with one method fails, the next
              method is used.  If no method succeeds, the user is
              denied access.

              An empty user-authentication-order leaf-list still allows
              authentication of users using mechanisms that do not
              involve a password.

              If the 'radius-authentication' feature is advertised by
              the NETCONF server, the 'radius' identity can be added to
              this list.

              If the 'local-users' feature is advertised by the
              NETCONF server, the 'local-users' identity can be
              added to this list.";
         }

         list user {
           if-feature local-users;
           key name;
           description
             "The list of local users configured on this device.";

           leaf name {
             type string;
             description
              "The user name string identifying this entry.";
           }
           leaf password {
             type ianach:crypt-hash;
             description
               "The password for this entry.";
           }
           list authorized-key {
             key name;
             description
               "A list of public SSH keys for this user.  These keys
                are allowed for SSH authentication, as described in
                RFC 4253.";
             reference
               "RFC 4253: The Secure Shell (SSH) Transport Layer
                          Protocol";

             leaf name {
               type string;
               description
                 "An arbitrary name for the SSH key.";
             }

             leaf algorithm {
               type string;
               mandatory true;
               description
                 "The public key algorithm name for this SSH key.

                  Valid values are the values in the IANA 'Secure Shell
                  (SSH) Protocol Parameters' registry, Public Key
                  Algorithm Names.";
               reference
                 "IANA 'Secure Shell (SSH) Protocol Parameters'
                  registry, Public Key Algorithm Names";
             }
             leaf key-data {
               type binary;
               mandatory true;
               description
                 "The binary public key data for this SSH key, as
                  specified by RFC 4253, Section 6.6, i.e.:

                    string    certificate or public key format
                              identifier
                    byte[n]   key/certificate data.";
               reference
                 "RFC 4253: The Secure Shell (SSH) Transport Layer
                            Protocol";
             }
           }
         }
       }
    }

    /*
     * Operational state data nodes
     */

    container system-state {
      config false;
      description
        "System group operational state.";

      container platform {
        description
          "Contains vendor-specific information for
           identifying the system platform and operating system.";
        reference
          "IEEE Std 1003.1-2008 - sys/utsname.h";

        leaf os-name {
          type string;
          description
            "The name of the operating system in use -
             for example, 'Linux'.";
          reference
            "IEEE Std 1003.1-2008 - utsname.sysname";
        }
        leaf os-release {
          type string;
          description
            "The current release level of the operating
             system in use.  This string MAY indicate
             the OS source code revision.";
          reference
            "IEEE Std 1003.1-2008 - utsname.release";
        }
        leaf os-version {
          type string;
          description
            "The current version level of the operating
             system in use.  This string MAY indicate
             the specific OS build date and target variant
             information.";
          reference
            "IEEE Std 1003.1-2008 - utsname.version";
        }
        leaf machine {
          type string;
          description
            "A vendor-specific identifier string representing
             the hardware in use.";
          reference
            "IEEE Std 1003.1-2008 - utsname.machine";
        }
      }

      container clock {
        description
          "Monitoring of the system date and time properties.";

        leaf current-datetime {
          type yang:date-and-time;
          description
            "The current system date and time.";
        }

        leaf boot-datetime {
          type yang:date-and-time;
          description
            "The system date and time when the system last restarted.";
        }
      }
    }

    rpc set-current-datetime {
      nacm:default-deny-all;
      description
        "Set the /system-state/clock/current-datetime leaf
         to the specified value.

         If the system is using NTP (i.e., /system/ntp/enabled
         is set to 'true'), then this operation will fail with
         error-tag 'operation-failed' and error-app-tag value of
         'ntp-active'.";
      input {
        leaf current-datetime {
          type yang:date-and-time;
          mandatory true;
          description
            "The current system date and time.";
        }
      }
    }

    rpc system-restart {
      nacm:default-deny-all;
      description
        "Request that the entire system be restarted immediately.
         A server SHOULD send an rpc reply to the client before
         restarting the system.";
    }

    rpc system-shutdown {
      nacm:default-deny-all;
      description
        "Request that the entire system be shut down immediately.
         A server SHOULD send an rpc reply to the client before
         shutting down the system.";
    }

  }

   <CODE ENDS>

7. IANA Considerations

   IANA has created an IANA-maintained YANG module called
   "iana-crypt-hash", based on the contents of Section 5, which will
   allow for new hash algorithms to be added to the type "crypt-hash".
   The registration procedure will be Expert Review, as defined by
   [RFC5226].

   This document registers two URIs in the "IETF XML Registry"
   [RFC3688].  Following the format in RFC 3688, the following
   registrations have been made.

      URI: urn:ietf:params:xml:ns:yang:iana-crypt-hash
      Registrant Contact: The IESG.
      XML: N/A; the requested URI is an XML namespace.

      URI: urn:ietf:params:xml:ns:yang:ietf-system
      Registrant Contact: The IESG.
      XML: N/A; the requested URI is an XML namespace.

   This document registers two YANG modules in the "YANG Module Names"
   registry [RFC6020].

      name: iana-crypt-hash
      namespace: urn:ietf:params:xml:ns:yang:iana-crypt-hash
      prefix: ianach
      reference: RFC 7317

      name: ietf-system
      namespace: urn:ietf:params:xml:ns:yang:ietf-system
      prefix: sys
      reference: RFC 7317

8. Security Considerations

   The YANG modules defined in this memo are designed to be accessed via
   the NETCONF protocol [RFC6241].  The lowest NETCONF layer is the
   secure transport layer and the mandatory to implement secure
   transport is SSH [RFC6242].  The NETCONF access control model
   [RFC6536] provides the means to restrict access for particular
   NETCONF users to a pre-configured subset of all available NETCONF
   protocol operations and content.

   There are a number of data nodes defined in the "ietf-system" YANG
   module which 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:

   o  /system/clock/timezone: This choice contains the objects used to
      control the time zone used by the device.

   o  /system/ntp: This container contains the objects used to control
      the Network Time Protocol servers used by the device.

   o  /system/dns-resolver: This container contains the objects used to
      control the Domain Name System servers used by the device.

   o  /system/radius: This container contains the objects used to
      control the Remote Authentication Dial-In User Service servers
      used by the device.

   o  /system/authentication/user-authentication-order: This leaf
      controls how user login attempts are authenticated by the device.

   o  /system/authentication/user: This list contains the local users
      enabled on the system.

   Some of the readable data nodes in the "ietf-system" 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:

   o  /system/platform: This container has objects that may help
      identify the specific NETCONF server and/or operating system
      implementation used on the device.

   o  /system/authentication/user: This list has objects that may help
      identify the specific user names and password information in use
      on the device.

   Some of the RPC operations in the "ietf-system" 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:

   o  set-current-datetime: Changes the current date and time on the
      device.

   o  system-restart: Reboots the device.

   o  system-shutdown: Shuts down the device.

   Since this document describes the use of RADIUS for purposes of
   authentication, it is vulnerable to all of the threats that are
   present in other RADIUS applications.  For a discussion of such
   threats, see [RFC2865] and [RFC3162], and Section 4 of [RFC3579].

   This document provides configuration parameters for SSH's "publickey"
   and "password" authentication mechanisms.  Section 9.4 of [RFC4251]
   and Section 11 of [RFC4252] discuss security considerations for these
   mechanisms.

   The "iana-crypt-hash" YANG module defines a type "crypt-hash" that
   can be used to store MD5 hashes.  [RFC6151] discusses security
   considerations for MD5.  The usage of MD5 is NOT RECOMMENDED.

9. References

9.1. Normative References

   [FIPS.180-4.2012]
              National Institute of Standards and Technology, "Secure
              Hash Standard (SHS)", FIPS PUB 180-4, March 2012,
              <http://csrc.nist.gov/publications/fips/fips180-4/
              fips-180-4.pdf>.

   [IEEE-1003.1-2008]
              Institute of Electrical and Electronics Engineers,
              "POSIX.1-2008", IEEE Standard 1003.1, March 2008.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC1321]  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
              April 1992.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
              "Remote Authentication Dial In User Service (RADIUS)",
              RFC 2865, June 2000.

   [RFC3162]  Aboba, B., Zorn, G., and D. Mitton, "RADIUS and IPv6",
              RFC 3162, August 2001.

   [RFC3418]  Presuhn, R., "Management Information Base (MIB) for the
              Simple Network Management Protocol (SNMP)", STD 62,
              RFC 3418, December 2002.

   [RFC4251]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Protocol Architecture", RFC 4251, January 2006.

   [RFC4252]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Authentication Protocol", RFC 4252, January 2006.

   [RFC4253]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Transport Layer Protocol", RFC 4253, January 2006.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5607]  Nelson, D. and G. Weber, "Remote Authentication Dial-In
              User Service (RADIUS) Authorization for Network Access
              Server (NAS) Management", RFC 5607, July 2009.

   [RFC5966]  Bellis, R., "DNS Transport over TCP - Implementation
              Requirements", RFC 5966, August 2010.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010.

   [RFC6151]  Turner, S. and L. Chen, "Updated Security Considerations
              for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
              RFC 6151, March 2011.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, June 2011.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, June 2011.

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536,
              March 2012.

   [RFC6991]  Schoenwaelder, J., "Common YANG Data Types", RFC 6991,
              July 2013.

9.2. Informative References

   [RFC3579]  Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication
              Dial In User Service) Support For Extensible
              Authentication Protocol (EAP)", RFC 3579, September 2003.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

   [RFC6557]  Lear, E. and P. Eggert, "Procedures for Maintaining the
              Time Zone Database", BCP 175, RFC 6557, February 2012.

Authors' Addresses

   Andy Bierman
   YumaWorks

   EMail: andy@yumaworks.com

   Martin Bjorklund
   Tail-f Systems

   EMail: mbj@tail-f.com