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+  module ietf-yang-types {
+
+    yang-version 1;
+
+    namespace
+      "urn:ietf:params:xml:ns:yang:ietf-yang-types";
+
+    prefix yang;
+
+    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: David Kessens
+              <mailto:david.kessens@nsn.com>
+
+    WG Chair: Juergen Schoenwaelder
+              <mailto:j.schoenwaelder@jacobs-university.de>
+
+    Editor:   Juergen Schoenwaelder
+              <mailto:j.schoenwaelder@jacobs-university.de>";
+
+    description
+      "This module contains a collection of generally useful derived
+    YANG data types.
+
+    Copyright (c) 2013 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 6991; see
+    the RFC itself for full legal notices.";
+
+    revision "2013-07-15" {
+      description
+        "This revision adds the following new data types:
+      - yang-identifier
+      - hex-string
+      - uuid
+      - dotted-quad";
+      reference
+        "RFC 6991: Common YANG Data Types";
+
+    }
+
+    revision "2010-09-24" {
+      description "Initial revision.";
+      reference
+        "RFC 6021: Common YANG Data Types";
+
+    }
+
+
+    typedef counter32 {
+      type uint32;
+      description
+        "The counter32 type represents a non-negative integer
+      that monotonically increases until it reaches a
+      maximum value of 2^32-1 (4294967295 decimal), when it
+      wraps around and starts increasing again from zero.
+
+      Counters have no defined 'initial' value, and thus, a
+      single value of a counter has (in general) no information
+      content.  Discontinuities in the monotonically increasing
+      value normally occur at re-initialization of the
+      management system, and at other times as specified in the
+      description of a schema node using this type.  If such
+      other times can occur, for example, the creation of
+      a schema node of type counter32 at times other than
+      re-initialization, then a corresponding schema node
+      should be defined, with an appropriate type, to indicate
+      the last discontinuity.
+
+      The counter32 type should not be used for configuration
+      schema nodes.  A default statement SHOULD NOT be used in
+      combination with the type counter32.
+
+      In the value set and its semantics, this type is equivalent
+      to the Counter32 type of the SMIv2.";
+      reference
+        "RFC 2578: Structure of Management Information Version 2
+        	  (SMIv2)";
+
+    }
+
+    typedef zero-based-counter32 {
+      type counter32;
+      default "0";
+      description
+        "The zero-based-counter32 type represents a counter32
+      that has the defined 'initial' value zero.
+
+      A schema node of this type will be set to zero (0) on creation
+      and will thereafter increase monotonically until it reaches
+      a maximum value of 2^32-1 (4294967295 decimal), when it
+      wraps around and starts increasing again from zero.
+
+      Provided that an application discovers a new schema node
+      of this type within the minimum time to wrap, it can use the
+      'initial' value as a delta.  It is important for a management
+      station to be aware of this minimum time and the actual time
+      between polls, and to discard data if the actual time is too
+      long or there is no defined minimum time.
+
+      In the value set and its semantics, this type is equivalent
+      to the ZeroBasedCounter32 textual convention of the SMIv2.";
+      reference
+        "RFC 4502: Remote Network Monitoring Management Information
+        	  Base Version 2";
+
+    }
+
+    typedef counter64 {
+      type uint64;
+      description
+        "The counter64 type represents a non-negative integer
+      that monotonically increases until it reaches a
+      maximum value of 2^64-1 (18446744073709551615 decimal),
+      when it wraps around and starts increasing again from zero.
+
+      Counters have no defined 'initial' value, and thus, a
+      single value of a counter has (in general) no information
+      content.  Discontinuities in the monotonically increasing
+      value normally occur at re-initialization of the
+      management system, and at other times as specified in the
+      description of a schema node using this type.  If such
+      other times can occur, for example, the creation of
+      a schema node of type counter64 at times other than
+      re-initialization, then a corresponding schema node
+      should be defined, with an appropriate type, to indicate
+      the last discontinuity.
+
+      The counter64 type should not be used for configuration
+      schema nodes.  A default statement SHOULD NOT be used in
+      combination with the type counter64.
+
+      In the value set and its semantics, this type is equivalent
+      to the Counter64 type of the SMIv2.";
+      reference
+        "RFC 2578: Structure of Management Information Version 2
+        	  (SMIv2)";
+
+    }
+
+    typedef zero-based-counter64 {
+      type counter64;
+      default "0";
+      description
+        "The zero-based-counter64 type represents a counter64 that
+      has the defined 'initial' value zero.
+
+
+
+
+      A schema node of this type will be set to zero (0) on creation
+      and will thereafter increase monotonically until it reaches
+      a maximum value of 2^64-1 (18446744073709551615 decimal),
+      when it wraps around and starts increasing again from zero.
+
+      Provided that an application discovers a new schema node
+      of this type within the minimum time to wrap, it can use the
+      'initial' value as a delta.  It is important for a management
+      station to be aware of this minimum time and the actual time
+      between polls, and to discard data if the actual time is too
+      long or there is no defined minimum time.
+
+      In the value set and its semantics, this type is equivalent
+      to the ZeroBasedCounter64 textual convention of the SMIv2.";
+      reference
+        "RFC 2856: Textual Conventions for Additional High Capacity
+        	  Data Types";
+
+    }
+
+    typedef gauge32 {
+      type uint32;
+      description
+        "The gauge32 type represents a non-negative integer, which
+      may increase or decrease, but shall never exceed a maximum
+      value, nor fall below a minimum value.  The maximum value
+      cannot be greater than 2^32-1 (4294967295 decimal), and
+      the minimum value cannot be smaller than 0.  The value of
+      a gauge32 has its maximum value whenever the information
+      being modeled is greater than or equal to its maximum
+      value, and has its minimum value whenever the information
+      being modeled is smaller than or equal to its minimum value.
+      If the information being modeled subsequently decreases
+      below (increases above) the maximum (minimum) value, the
+      gauge32 also decreases (increases).
+
+      In the value set and its semantics, this type is equivalent
+      to the Gauge32 type of the SMIv2.";
+      reference
+        "RFC 2578: Structure of Management Information Version 2
+        	  (SMIv2)";
+
+    }
+
+    typedef gauge64 {
+      type uint64;
+      description
+        "The gauge64 type represents a non-negative integer, which
+      may increase or decrease, but shall never exceed a maximum
+      value, nor fall below a minimum value.  The maximum value
+      cannot be greater than 2^64-1 (18446744073709551615), and
+      the minimum value cannot be smaller than 0.  The value of
+      a gauge64 has its maximum value whenever the information
+      being modeled is greater than or equal to its maximum
+      value, and has its minimum value whenever the information
+      being modeled is smaller than or equal to its minimum value.
+      If the information being modeled subsequently decreases
+      below (increases above) the maximum (minimum) value, the
+      gauge64 also decreases (increases).
+
+      In the value set and its semantics, this type is equivalent
+      to the CounterBasedGauge64 SMIv2 textual convention defined
+      in RFC 2856";
+      reference
+        "RFC 2856: Textual Conventions for Additional High Capacity
+        	  Data Types";
+
+    }
+
+    typedef object-identifier {
+      type string {
+        pattern
+          '(([0-1](\.[1-3]?[0-9]))|(2\.(0|([1-9]\d*))))(\.(0|([1-9]\d*)))*';
+      }
+      description
+        "The object-identifier type represents administratively
+      assigned names in a registration-hierarchical-name tree.
+
+      Values of this type are denoted as a sequence of numerical
+      non-negative sub-identifier values.  Each sub-identifier
+      value MUST NOT exceed 2^32-1 (4294967295).  Sub-identifiers
+      are separated by single dots and without any intermediate
+      whitespace.
+
+      The ASN.1 standard restricts the value space of the first
+      sub-identifier to 0, 1, or 2.  Furthermore, the value space
+      of the second sub-identifier is restricted to the range
+      0 to 39 if the first sub-identifier is 0 or 1.  Finally,
+      the ASN.1 standard requires that an object identifier
+      has always at least two sub-identifiers.  The pattern
+      captures these restrictions.
+
+      Although the number of sub-identifiers is not limited,
+      module designers should realize that there may be
+      implementations that stick with the SMIv2 limit of 128
+      sub-identifiers.
+
+      This type is a superset of the SMIv2 OBJECT IDENTIFIER type
+      since it is not restricted to 128 sub-identifiers.  Hence,
+      this type SHOULD NOT be used to represent the SMIv2 OBJECT
+      IDENTIFIER type; the object-identifier-128 type SHOULD be
+      used instead.";
+      reference
+        "ISO9834-1: Information technology -- Open Systems
+        Interconnection -- Procedures for the operation of OSI
+        Registration Authorities: General procedures and top
+        arcs of the ASN.1 Object Identifier tree";
+
+    }
+
+    typedef object-identifier-128 {
+      type object-identifier {
+        pattern '\d*(\.\d*){1,127}';
+      }
+      description
+        "This type represents object-identifiers restricted to 128
+      sub-identifiers.
+
+      In the value set and its semantics, this type is equivalent
+      to the OBJECT IDENTIFIER type of the SMIv2.";
+      reference
+        "RFC 2578: Structure of Management Information Version 2
+        	  (SMIv2)";
+
+    }
+
+    typedef yang-identifier {
+      type string {
+        length "1..max";
+        pattern '[a-zA-Z_][a-zA-Z0-9\-_.]*';
+        pattern
+          '.|..|[^xX].*|.[^mM].*|..[^lL].*';
+      }
+      description
+        "A YANG identifier string as defined by the 'identifier'
+       rule in Section 12 of RFC 6020.  An identifier must
+       start with an alphabetic character or an underscore
+       followed by an arbitrary sequence of alphabetic or
+       numeric characters, underscores, hyphens, or dots.
+
+       A YANG identifier MUST NOT start with any possible
+       combination of the lowercase or uppercase character
+       sequence 'xml'.";
+      reference
+        "RFC 6020: YANG - A Data Modeling Language for the Network
+        	  Configuration Protocol (NETCONF)";
+
+    }
+
+    typedef date-and-time {
+      type string {
+        pattern
+          '\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(\.\d+)?(Z|[\+\-]\d{2}:\d{2})';
+      }
+      description
+        "The date-and-time type is a profile of the ISO 8601
+      standard for representation of dates and times using the
+      Gregorian calendar.  The profile is defined by the
+      date-time production in Section 5.6 of RFC 3339.
+
+      The date-and-time type is compatible with the dateTime XML
+      schema type with the following notable exceptions:
+
+      (a) The date-and-time type does not allow negative years.
+
+      (b) The date-and-time time-offset -00:00 indicates an unknown
+          time zone (see RFC 3339) while -00:00 and +00:00 and Z
+          all represent the same time zone in dateTime.
+
+      (c) The canonical format (see below) of data-and-time values
+          differs from the canonical format used by the dateTime XML
+          schema type, which requires all times to be in UTC using
+          the time-offset 'Z'.
+
+      This type is not equivalent to the DateAndTime textual
+      convention of the SMIv2 since RFC 3339 uses a different
+      separator between full-date and full-time and provides
+      higher resolution of time-secfrac.
+
+      The canonical format for date-and-time values with a known time
+      zone uses a numeric time zone offset that is calculated using
+      the device's configured known offset to UTC time.  A change of
+      the device's offset to UTC time will cause date-and-time values
+      to change accordingly.  Such changes might happen periodically
+      in case a server follows automatically daylight saving time
+      (DST) time zone offset changes.  The canonical format for
+      date-and-time values with an unknown time zone (usually
+      referring to the notion of local time) uses the time-offset
+      -00:00.";
+      reference
+        "RFC 3339: Date and Time on the Internet: Timestamps
+         RFC 2579: Textual Conventions for SMIv2
+        XSD-TYPES: XML Schema Part 2: Datatypes Second Edition";
+
+    }
+
+    typedef timeticks {
+      type uint32;
+      description
+        "The timeticks type represents a non-negative integer that
+      represents the time, modulo 2^32 (4294967296 decimal), in
+      hundredths of a second between two epochs.  When a schema
+      node is defined that uses this type, the description of
+      the schema node identifies both of the reference epochs.
+
+      In the value set and its semantics, this type is equivalent
+      to the TimeTicks type of the SMIv2.";
+      reference
+        "RFC 2578: Structure of Management Information Version 2
+        	  (SMIv2)";
+
+    }
+
+    typedef timestamp {
+      type timeticks;
+      description
+        "The timestamp type represents the value of an associated
+      timeticks schema node at which a specific occurrence
+      happened.  The specific occurrence must be defined in the
+      description of any schema node defined using this type.  When
+      the specific occurrence occurred prior to the last time the
+      associated timeticks attribute was zero, then the timestamp
+      value is zero.  Note that this requires all timestamp values
+      to be reset to zero when the value of the associated timeticks
+      attribute reaches 497+ days and wraps around to zero.
+
+      The associated timeticks schema node must be specified
+      in the description of any schema node using this type.
+
+      In the value set and its semantics, this type is equivalent
+      to the TimeStamp textual convention of the SMIv2.";
+      reference
+        "RFC 2579: Textual Conventions for SMIv2";
+
+    }
+
+    typedef phys-address {
+      type string {
+        pattern
+          '([0-9a-fA-F]{2}(:[0-9a-fA-F]{2})*)?';
+      }
+      description
+        "Represents media- or physical-level addresses represented
+      as a sequence octets, each octet represented by two hexadecimal
+      numbers.  Octets are separated by colons.  The canonical
+      representation uses lowercase characters.
+
+      In the value set and its semantics, this type is equivalent
+      to the PhysAddress textual convention of the SMIv2.";
+      reference
+        "RFC 2579: Textual Conventions for SMIv2";
+
+    }
+
+    typedef mac-address {
+      type string {
+        pattern
+          '[0-9a-fA-F]{2}(:[0-9a-fA-F]{2}){5}';
+      }
+      description
+        "The mac-address type represents an IEEE 802 MAC address.
+      The canonical representation uses lowercase characters.
+
+      In the value set and its semantics, this type is equivalent
+      to the MacAddress textual convention of the SMIv2.";
+      reference
+        "IEEE 802: IEEE Standard for Local and Metropolitan Area
+        	  Networks: Overview and Architecture
+         RFC 2579: Textual Conventions for SMIv2";
+
+    }
+
+    typedef xpath1.0 {
+      type string;
+      description
+        "This type represents an XPATH 1.0 expression.
+
+      When a schema node is defined that uses this type, the
+      description of the schema node MUST specify the XPath
+      context in which the XPath expression is evaluated.";
+      reference
+        "XPATH: XML Path Language (XPath) Version 1.0";
+
+    }
+
+    typedef hex-string {
+      type string {
+        pattern
+          '([0-9a-fA-F]{2}(:[0-9a-fA-F]{2})*)?';
+      }
+      description
+        "A hexadecimal string with octets represented as hex digits
+      separated by colons.  The canonical representation uses
+      lowercase characters.";
+    }
+
+    typedef uuid {
+      type string {
+        pattern
+          '[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}';
+      }
+      description
+        "A Universally Unique IDentifier in the string representation
+      defined in RFC 4122.  The canonical representation uses
+      lowercase characters.
+
+      The following is an example of a UUID in string representation:
+      f81d4fae-7dec-11d0-a765-00a0c91e6bf6
+      ";
+      reference
+        "RFC 4122: A Universally Unique IDentifier (UUID) URN
+        	  Namespace";
+
+    }
+
+    typedef dotted-quad {
+      type string {
+        pattern
+          '(([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])';
+      }
+      description
+        "An unsigned 32-bit number expressed in the dotted-quad
+       notation, i.e., four octets written as decimal numbers
+       and separated with the '.' (full stop) character.";
+    }
+  }  // module ietf-yang-types
+