module ietf-system {

    yang-version 1;

    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";

    }


    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";

    }

    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.";
    }

    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)";

    }

    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-name
          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.";
          }
        }  // choice timezone
      }  // container clock

      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.";
            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.";
              }
            }  // container udp
          }  // choice transport

          leaf association-type {
            type enumeration {
              enum "server" {
                value 0;
                description
                  "Use client association mode.  This device
will not provide synchronization to the
configured NTP server.";
              }
              enum "peer" {
                value 1;
                description
                  "Use symmetric active association mode.
This device may provide synchronization
to the configured NTP server.";
              }
              enum "pool" {
                value 2;
                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.";
          }
        }  // list server
      }  // container ntp

      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.";
            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 udp-and-tcp
          }  // choice transport
        }  // list 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 options
      }  // container dns-resolver

      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.";
            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 {
                nacm:default-deny-all;
                type string;
                mandatory true;
                description
                  "The shared secret, which is known to both the
RADIUS client and server.";
                reference
                  "RFC 2865: Remote Authentication Dial In User
                  	  Service (RADIUS)";

              }
            }  // container udp
          }  // choice transport

          leaf authentication-type {
            type identityref {
              base radius-authentication-type;
            }
            default "radius-pap";
            description
              "The authentication type requested from the RADIUS
server.";
          }
        }  // list 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 options
      }  // container radius

      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";

            }
          }  // list authorized-key
        }  // list user

        container tls {
          container trusted-ca-certs {
            description
              "A list of Certificate Authority (CA) certificates that a
NETCONF server can use to authenticate a NETCONF client's
certificate.  A client's certificate is authenticated if
its Issuer matches one of the configured trusted CA
certificates.";
            leaf-list trusted-ca-cert {
              type binary;
              description
                "The binary certificate structure, as
specified by RFC 5246, Section 7.4.6, i.e.,:

  opaque ASN.1Cert<1..2^24>;

";
              reference
                "RFC 5246: The Transport Layer Security (TLS)
                	  Protocol Version 1.2";

            }
          }  // container trusted-ca-certs

          container trusted-client-certs {
            description
              "A list of client certificates that a NETCONF server can
use to authenticate a NETCONF client's certificate.  A
client's certificate is authenticated if it is an exact
match to one of the configured trusted client certificates.";
            leaf-list trusted-client-cert {
              type binary;
              description
                "The binary certificate structure, as
specified by RFC 5246, Section 7.4.6, i.e.,:

  opaque ASN.1Cert<1..2^24>;

";
              reference
                "RFC 5246: The Transport Layer Security (TLS)
                	  Protocol Version 1.2";

            }
          }  // container trusted-client-certs

          container cert-maps {
            if-feature tls-map-certificates;
            description
              "The cert-maps container is used by a NETCONF server to
map the NETCONF client's presented X.509 certificate to
a NETCONF username.

If no matching and valid cert-to-name list entry can be
found, then the NETCONF server MUST close the connection,
and MUST NOT accept NETCONF messages over it.";
            list cert-to-name {
              key "id";
              description
                "This list defines how certificates are mapped to names.
The name is derived by considering each cert-to-name
list entry in order.  The cert-to-name entry's fingerprint
determines whether the list entry is a match:

1) If the cert-to-name list entry's fingerprint value
   matches that of the presented certificate, then consider
   the list entry a successful match.

2) If the cert-to-name list entry's fingerprint value
   matches that of a locally held copy of a trusted CA
   certificate, and that CA certificate was part of the CA
   certificate chain to the presented certificate, then
   consider the list entry a successful match.

Once a matching cert-to-name list entry has been found, the
map-type is used to determine how the name associated with
the certificate should be determined.  See the map-type
leaf's description for details on determining the name value.
If it is impossible to determine a name from the cert-to-name
list entry's data combined with the data presented in the
certificate, then additional cert-to-name list entries MUST
be searched to look for another potential match.

Security administrators are encouraged to make use of
certificates with subjectAltName fields that can be mapped to
names so that a single root CA certificate can allow all
child certificates' subjectAltName fields to map directly to
a name via a 1:1 transformation.";
              reference
                "RFC 6353: Transport Layer Security (TLS) Transport Model
                  for the Simple Network Management Protocol (SNMP).
                  SNMP-TLS-TM-MIB.snmpTlstmCertToTSNEntry";

              leaf id {
                type uint32;
                description
                  "The id specifies the order in which the entries in the
cert-to-name list are searched.  Entries with lower
numbers are searched first.";
                reference
                  "RFC 6353: Transport Layer Security (TLS) Transport Model
                    for the Simple Network Management Protocol
                    (SNMP).
                    SNMP-TLS-TM-MIB.snmpTlstmCertToTSNID";

              }

              leaf fingerprint {
                type x509c2n:tls-fingerprint;
                mandatory true;
                description
                  "Specifies a value with which the fingerprint of the
full certificate presented by the peer is compared.  If
the fingerprint of the full certificate presented by the
peer does not match the fingerprint configured, then the
entry is skipped, and the search for a match continues.";
                reference
                  "RFC 6353: Transport Layer Security (TLS) Transport Model
                    for the Simple Network Management Protocol
                    (SNMP).
                    SNMP-TLS-TM-MIB.snmpTlstmCertToTSNFingerprint";

              }

              leaf map-type {
                type identityref {
                  base cert-to-name;
                }
                mandatory true;
                description
                  "Specifies the algorithm used to map the certificate
presented by the peer to a name.

Mappings that need additional configuration objects should
use the 'when' statement to make them conditional based on
the map-type.";
                reference
                  "RFC 6353: Transport Layer Security (TLS) Transport Model
                    for the Simple Network Management Protocol
                    (SNMP).
                    SNMP-TLS-TM-MIB.snmpTlstmCertToTSNMapType";

              }

              leaf name {
                when
                  "../map-type = 'x509c2n:specified'";
                type string;
                mandatory true;
                description
                  "Directly specifies the NETCONF username when the
map-type is 'specified'.";
                reference
                  "RFC 6353: Transport Layer Security (TLS) Transport Model
                    for the Simple Network Management Protocol
                    (SNMP).
                    SNMP-TLS-TM-MIB.snmpTlstmCertToTSNData";

              }
            }  // list cert-to-name
          }  // container cert-maps

          container psk-maps {
            if-feature tls-map-pre-shared-keys;
            description
              "During the TLS Handshake, the client indicates which
key to use by including a PSK identity in the TLS
ClientKeyExchange message. On the NETCONF server side,
this PSK identity is used to look up an entry in the psk-map
list. If such an entry is found, and the pre-shared keys
match, then the client is authenticated. The NETCONF
server uses the value from the user-name leaf in the
psk-map list as the NETCONF username.  If the NETCONF
server cannot find an entry in the psk-map list, or if
the pre-shared keys do not match, then the NETCONF
server terminates the connection.";
            reference
              "RFC 4279: Pre-Shared Key Ciphersuites for Transport Layer
              	  Security (TLS)";

            list psk-map {
              key "psk-identity";
              leaf psk-identity {
                type string;
                description
                  "The PSK identity encoded as a UTF-8 string. For
details how certain common PSK identity formats can
be encoded in UTF-8, see section 5.1. of RFC 4279.";
                reference
                  "RFC 4279: Pre-Shared Key Ciphersuites for Transport
                  Layer Security (TLS)";

              }

              leaf user-name {
                type nacm:user-name-type;
                mandatory true;
                description
                  "The NETCONF username associated with this PSK
identity.";
              }

              leaf not-valid-before {
                type yang:date-and-time;
                description
                  "This PSK identity is not valid before the given date
and time.";
              }

              leaf not-valid-after {
                type yang:date-and-time;
                description
                  "This PSK identity is not valid after the given date
and time.";
              }

              leaf key {
                nacm:default-deny-all;
                type yang:hex-string;
                mandatory true;
                description
                  "The key associated with the PSK identity";
                reference
                  "RFC 4279: Pre-Shared Key Ciphersuites for Transport
                  Layer Security (TLS)";

              }
            }  // list psk-map
          }  // container psk-maps
        }  // container tls
      }  // container authentication

      container tacacs-plus {
        must
          "not(derived-from-or-self(../sys:authentication/sys:user-authentication-order, 'tacacs-plus')) or bit-is-set(server/server-type,'authentication')" {
          error-message
            "When 'tacacs-plus' is used as a system authentication method, a TACACS+ authentication server must be configured.";
          description
            "When 'tacacs-plus' is used as an authentication method,
a TACACS+ server must be configured.";
        }
        description
          "Container for TACACS+ configurations and operations.";
        list server {
          key "name";
          ordered-by user;
          description
            "List of TACACS+ servers used by the device.";
          leaf name {
            type string;
            description
              "An arbitrary name for the TACACS+ server.";
          }

          leaf server-type {
            type tacacs-plus-server-type;
            mandatory true;
            description
              "Server type: authentication/authorization/accounting and
various combinations.";
          }

          leaf address {
            type inet:host;
            mandatory true;
            description
              "The address of the TACACS+ server.";
          }

          leaf port {
            type inet:port-number;
            default "49";
            description
              "The port number of TACACS+ Server port.";
          }

          choice security {
            mandatory true;
            description
              "Security mechanism between TACACS+ client and server.
This is modeled as a YANG 'choice' so that it can be
augmented by a YANG module in a backwards-compatible
manner.";
            leaf shared-secret {
              nacm:default-deny-all;
              type string {
                length "1..max";
              }
              description
                "The shared secret, which is known to both the
TACACS+ client and server.  TACACS+ server
administrators SHOULD configure a shared secret with
a minimum length of 16 characters.
It is highly recommended that this shared secret is
at least 32 characters long and sufficiently complex
with a mix of different character types,
i.e., upper case, lower case, numeric, and
punctuation.  Note that this security mechanism is
best described as 'obfuscation' and not 'encryption'
as it does not provide any meaningful integrity,
privacy, or replay protection.";
              reference
                "RFC 8907: The TACACS+ Protocol";

            }
          }  // choice security

          choice source-type {
            description
              "The source address type for outbound TACACS+ packets.";
            leaf source-ip {
              type inet:ip-address;
              description
                "Specifies source IP address for TACACS+ outbound
packets.";
            }
            leaf source-interface {
              type if:interface-ref;
              description
                "Specifies the interface from which the IP address
is derived for use as the source for the outbound
TACACS+ packet.";
            }
          }  // choice source-type

          leaf vrf-instance {
            type leafref {
              path "/ni:network-instances/ni:network-instance/ni:name";
            }
            description
              "Specifies the VPN Routing and Forwarding (VRF) instance
to use to communicate with the TACACS+ server.";
            reference
              "RFC 8529: YANG Data Model for Network Instances";

          }

          leaf single-connection {
            type boolean;
            default "false";
            description
              "Indicates whether the Single Connection Mode is enabled
for the server.  By default, the Single Connection Mode
is disabled.";
          }

          leaf timeout {
            type uint16 {
              range "1..max";
            }
            units "seconds";
            default "5";
            description
              "The number of seconds the device will wait for a
response from each TACACS+ server before trying with a
different server.";
          }

          container statistics {
            config false;
            description
              "A collection of server-related statistics objects.";
            leaf connection-opens {
              type yang:counter64;
              description
                "Number of new connection requests sent to the server,
e.g., socket open.";
            }

            leaf connection-closes {
              type yang:counter64;
              description
                "Number of connection close requests sent to the server,
e.g., socket close.";
            }

            leaf connection-aborts {
              type yang:counter64;
              description
                "Number of aborted connections to the server.  These do
not include connections that are closed gracefully.";
            }

            leaf connection-failures {
              type yang:counter64;
              description
                "Number of connection failures to the server.";
            }

            leaf connection-timeouts {
              type yang:counter64;
              description
                "Number of connection timeouts to the server.";
            }

            leaf messages-sent {
              type yang:counter64;
              description
                "Number of messages sent to the server.";
            }

            leaf messages-received {
              type yang:counter64;
              description
                "Number of messages received from the server.";
            }

            leaf errors-received {
              type yang:counter64;
              description
                "Number of error messages received from the server.";
            }

            leaf sessions {
              type yang:counter64;
              description
                "Number of TACACS+ sessions completed with the server.
If the Single Connection Mode was NOT enabled, the number
of sessions is the same as the number of
'connection-closes'.  If the Mode was enabled, a single
TCP connection may contain multiple TACACS+ sessions.";
            }
          }  // container statistics
        }  // list server
      }  // container tacacs-plus
    }  // container system

    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 platform

      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.";
        }
      }  // container clock
    }  // container system-state

    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 set-current-datetime

    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-restart

    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.";
    }  // rpc system-shutdown
  }  // module ietf-system