NETMOD WG                                                 C. Wildes, Ed.
Internet-Draft                                           K. Koushik, Ed.
Intended status: Standards Track                      Cisco Systems Inc.
Expires: May 17, August 16, 2017                               February 14, 2017                                  November 13, 2016

               A YANG Data Model for Syslog Configuration
                   draft-ietf-netmod-syslog-model-11
                   draft-ietf-netmod-syslog-model-12

Abstract

   This document describes a data model for the configuration of syslog.

Status of This this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

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

   This Internet-Draft will expire on May 17, August 16, 2017.

Copyright Notice

   Copyright (c) 2016 2017 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) (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.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .   3  2
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .   3  2
   2.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . .   3  2
   3.  Design of the Syslog Model . . . . . . . . . . . . . . . . . .  3
     3.1.  Syslog Module  . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Syslog YANG Modules  . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  The ietf-syslog-types Module . . . . . . . . . . . . . . .  8
     4.2.  The ietf-syslog Module . . . . . . . . . . . . . . . . . . 14
   5.  Usage Examples . . . . . . . . . . . . . . . . . . . . . . .  26 . 25
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . .  28 . 26
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  28 26
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . .  29 27
     8.1.  Resource Constraints . . . . . . . . . . . . . . . . . .  29 . 27
     8.2.  Inappropriate Configuration  . . . . . . . . . . . . . . .  30 27
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . .  30 . 27
     9.1.  Normative References . . . . . . . . . . . . . . . . . .  30 . 27
     9.2.  Informative References . . . . . . . . . . . . . . . . .  30 . 28
   Appendix A. Implementor Guidelines . . . . . . . . . . . . . . .  31 . 28
     Appendix A.1.  Extending Facilities  . . . . . . . . . . . . . . . . . .  31 28
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . .  32 . 29

1.  Introduction

   Operating systems, processes and applications generate messages
   indicating their own status or the occurrence of events.  These
   messages are useful for managing and/or debugging the network and its
   services.  The BSD syslog protocol is a widely adopted protocol that
   is used for transmission and processing of the messages.

   Since each process, application and operating system was written
   somewhat independently, there is little uniformity to the content of
   syslog messages.  For this reason, no assumption is made upon the
   formatting or contents of the messages.  The protocol is simply
   designed to transport these event messages.  No acknowledgement of
   the receipt is made.

   Essentially, a syslog process receives messages (from the kernel,
   processes, applications or other syslog processes) and processes
   those.  The processing involves logging to a local file, displaying
   on console, user terminal, and/or relaying to syslog processes on other machines.
   The processing is determined by the "facility" that originated the
   message and the "severity" assigned to the message by the facility.

   We are using definitions of syslog protocol from [RFC5424] in this
   RFC.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

1.2.  Terminology

   The term "originator" is defined in [RFC5424]: an "originator"
   generates syslog content to be carried in a message.

   The terms "relay" and "collectors" are as defined in [RFC5424].

2.  Problem Statement
   This document defines a YANG [RFC6020] configuration data model that
   may be used to configure the syslog feature running on a system.
   YANG models can be used with network management protocols such as
   NETCONF [RFC6241] to install, manipulate, and delete the
   configuration of network devices.

   The data model makes use of the YANG "feature" construct which allows
   implementations to support only those syslog features that lie within
   their capabilities.

   This module can be used to configure the syslog application
   conceptual layers as implemented on the target system [RFC5424].

3.  Design of the Syslog Model

   The syslog model was designed by comparing various syslog features
   implemented by various vendors' in different implementations.

   This draft addresses the common leafs between implementations and
   creates a common model, which can be augmented with proprietary
   features, if necessary.  The base model is designed to be very simple
   for maximum flexibility.

   Optional features are used to specify functionality that is present
   in specific vendor configurations.

   Syslog consists of originators, and collectors.  The following digram
   diagram shows syslog messages flowing from an originator, to
   collectors where
   suppression filtering can take place.

   Many vendors extend the list of facilities available for logging in
   their implementation.  An example is included in Extending Facilities
   (Appendix A.1).

   Originators
     +-------------+  +-------------+  +-------------+  +-------------+
     |  Various    |  |     OS      |  |             |  |   Remote    |
     | Components  |  |   Kernel    |  | Line Cards  |  |   Servers   |
     +-------------+  +-------------+  +-------------+  +-------------+

     +-------------+  +-------------+  +-------------+  +-------------+
     |    SNMP     |  |  Interface  |  |   Standby   |  |   Syslog    |
     |   Events    |  |   Events    |  |  Supervisor |  |   Itself    |
     +-------------+  +-------------+  +-------------+  +-------------+

     |                                                                |
     +----------------------------------------------------------------+
                  |
                  |
                  |
                  |
          +-----------+------------+--------------+
          |
          +-------------+--------------+
          |             |              |
          v             v              v              |
   Collectors                           |
     +----------+
     +----------+ +----------+ +----------------+
     |          | | |  Log     | |  Log     |       | |Remote Relay(s)/|
     | Console  | |  Buffer  | |  File(s) | |Collector(s)    |
     +----------+ +----------+ +----------+       |
                                                  |
                                                +-+-------------+
                                                |               |
                                                v               v

                                        +----------------+ +-----------+
                                        |Remote Relay(s)/| |User       |
                                        |Collectors(s)   | |Sessions(s)| +----------------+ +-----------+

   Figure 1. Syslog Processing Flow

   The leaves in the base syslog model actions container correspond to
   each message collector:

      console
      log buffer
      log file(s)
      remote relay(s)/collector(s)
      user session(s).

   Within each action, a selector is used to filter syslog messages.  A
   selector consists of two parts: a list of one or more facility-severity matches, and
   and, if supported via the select-match feature, an optional regular
   expression pattern match that is performed on the SYSLOG-MSG field.

   Selector processing (input is syslog message):

       1. Loop through facility-list
          a. Facility match processing - continue to the next entry in
             the list if no match
          b. Severity compare processing - continue to the next list
             entry if no match
          c. Match - proceed with the action and exit further processing
       2. Process pattern match if specified and if a match proceed with
          the action

   The facility is one of a specific syslogtypes:syslog-facility, none, or all
   facilities.  None is a special case that can be used to
   disable an action.

   The severity is one of syslogtypes:severity, all severities, or none.
   None is a special case that can be used to disable a facility.  When
   filtering severity, the default comparison is that all messages of the
   specified severity and higher are selected to be logged.  This is
   shown in the model as ?default equals-or-higher?. "default equals-or-higher".  This behavior can
   be altered if the select-sev-compare select-adv-compare feature is enabled to specify: ?equals? to specify only a
   compare operatorn  and an action.  Compare operations are: "equals"
   to select messages with this single severity; ?not-equals? to ignore that
   severity; ?equals-or-higher? severity, or "equals-or-higher"
   to specify all select messages of the specified severity and higher.

   Optional features  Actions are used
   to specified functionality that is present
   in specific vendor configurations. log the message or block the message from being logged.

3.1.  Syslog Module

   A simplified graphical representation of the complete data tree is
   presented here.

   Each node is printed as:

   <status> <flags> <name> <opts> <type> <if-features>

   <status> is one of:

          +  for current
          x  for deprecated
          o  for obsolete

   <flags> is one of:

          rw  for configuration data
          ro  for non-configuration data
          -x  for rpcs
          -n  for notifications

   <name> is the name of the node

          (<name>) means that the node is a choice node
          :(<name>) means that the node is a case node

   If the node is augmented into the tree from another module, its name
   is printed as <prefix>:<name>.

   <opts> is one of:

          ?  for an optional leaf or choice
          !  for a presence container
          *  for a leaf-list or list
          [<keys>] for a list's keys

   <type> is the name of the type for leafs and leaf-lists

   If the type is a leafref, the type is printed as "-> TARGET", where
   TARGET is either the leafref path, with prefixed removed if possible.

   <if-features> is the list of features this node depends on, printed
   within curly brackets and a question mark "{...}?"
   module: ietf-syslog
      +--rw syslog!
         +--rw actions
            +--rw console! {console-action}?
            |  +--rw selector
            |     +--rw (selector-facility)
         |     |  +--:(facility)
         |     |  |  +--rw no-facilities?   empty
         |     |  +--:(name)
         |     |     +--rw facility-list* [facility] [facility severity]
            |     |  +--rw facility            union
            |     |  +--rw severity            union
            |     |  +--rw advanced-compare {select-adv-compare}?
            |     |     +--rw compare?   enumeration {select-sev-compare}?
            |     |     +--rw action?    enumeration
            |     +--rw pattern-match?   string {select-match}?
            +--rw buffer {buffer-action}? file {file-action}?
            |  +--rw selector
         | log-file* [name]
            |     +--rw (selector-facility)
         |  |  |  +--:(facility)
         |  |  | name               inet:uri
            |     +--rw no-facilities?   empty
         |  |  |  +--:(name)
         | selector
            |     |  +--rw facility-list* [facility] [facility severity]
            |     |  |  +--rw facility            union
            |     |  |  +--rw severity            union
            |     |  |  +--rw advanced-compare {select-adv-compare}?
            |     |  |     +--rw compare?   enumeration {select-sev-compare}?
            |     |  |     +--rw action?    enumeration
            |     |  +--rw pattern-match?   string {select-match}?
            |     +--rw structured-data?   boolean {structured-data}?
            |     +--rw buffer-limit-bytes?      uint64 {buffer-limit-bytes}? file-rotation
            |        +--rw buffer-limit-messages?   uint64 {buffer-limit-messages}?
         +--rw file number-of-files?   uint32 {file-limit-size}?
            |        +--rw log-file* [name] max-file-size?     uint32 {file-limit-size}?
            |        +--rw name               inet:uri
         |     +--rw selector
         |     |  +--rw (selector-facility)
         |     |  |  +--:(facility)
         |     |  |  |  +--rw no-facilities?   empty
         |     |  |  +--:(name)
         |     |  |     +--rw facility-list* [facility]
         |     |  |        +--rw facility    union
         |     |  |        +--rw severity    union
         |     |  |        +--rw compare?    enumeration {select-sev-compare}?
         |     |  +--rw pattern-match?   string {select-match}?
         |     +--rw structured-data?   boolean {structured-data}?
         |     +--rw file-rotation
         |        +--rw number-of-files?   uint32 {file-limit-size}?
         |        +--rw max-file-size?     uint64 {file-limit-size}?
         |        +--rw rollover?          uint32 {file-limit-duration}? rollover?          uint32 {file-limit-duration}?
            |        +--rw retention?         uint16         uint32 {file-limit-duration}?
            +--rw remote
         | {remote-action}?
               +--rw destination* [name]
         |
                  +--rw name                 string
         |
                  +--rw (transport)
                  |     |  +--:(tcp)
                  |  |  |  +--rw tcp
                  |  |  |     +--rw address?   inet:host
                  |  |  |     +--rw port?      inet:port-number
                  |     |  +--:(udp)
                  |     |     +--rw udp
                  |     |        +--rw address?   inet:host
                  |     |        +--rw port?      inet:port-number
         |
                  +--rw selector
                  |     |  +--rw (selector-facility)
         |     |  |  +--:(facility)
         |     |  |  |  +--rw no-facilities?   empty
         |     |  |  +--:(name)
         |     |  |  +--rw facility-list* [facility]
         | [facility severity]
                  |  |  +--rw facility            union
                  |  |  |  +--rw severity            union
                  |  |  +--rw advanced-compare {select-adv-compare}?
                  |  |     +--rw compare?   enumeration {select-sev-compare}?
                  |  |     +--rw action?    enumeration
                  |  +--rw pattern-match?   string {select-match}?
         |
                  +--rw structured-data?     boolean {structured-data}?
         |
                  +--rw facility-override?   identityref
         |
                  +--rw source-interface?    if:interface-ref
         | {remote-source-interface}?
                  +--rw signing-options! {signed-messages}?
         |
                     +--rw cert-initial-repeat    uint16
         |
                     +--rw cert-resend-delay      uint16
         |
                     +--rw cert-resend-count      uint16
         |
                     +--rw max-delay              uint16
         |
                     +--rw number-resends         uint16
         |
                     +--rw resend-delay           uint16
         |
                     +--rw resend-count           uint16
         +--rw session
            +--rw all-users!
            |  +--rw selector
            |     +--rw (selector-facility)
            |     |  +--:(facility)
            |     |  |  +--rw no-facilities?   empty
            |     |  +--:(name)
            |     |     +--rw facility-list* [facility]
            |     |        +--rw facility    union
            |     |        +--rw severity    union
            |     |        +--rw compare?    enumeration {select-sev-compare}?
            |     +--rw pattern-match?   string {select-match}?
            +--rw user* [name]
               +--rw name        string
               +--rw selector
                  +--rw (selector-facility)
                  |  +--:(facility)
                  |  |  +--rw no-facilities?   empty
                  |  +--:(name)
                  |     +--rw facility-list* [facility]
                  |        +--rw facility    union
                  |        +--rw severity    union
                  |        +--rw compare?    enumeration {select-sev-compare}?
                  +--rw pattern-match?   string {select-match}?

   Figure 2. ietf-syslog Module Tree

4.  Syslog YANG Modules

4.1.  The ietf-syslog-types Module

   This module references [RFC5424].

   <CODE BEGINS> file "ietf-syslog-types.yang"
   module ietf-syslog-types {
     namespace "urn:ietf:params:xml:ns:yang:ietf-syslog-types";
     prefix syslogtypes;

     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: Lou Berger
                  <mailto:lberger@labn.net>

        WG Chair: Kent Watsen
                  <mailto:kwatsen@juniper.net>

        Editor:   Kiran Agrahara Sreenivasa
                  <mailto:kkoushik@cisco.com>

        Editor:   Clyde Wildes
                  <mailto:cwildes@cisco.com>";
     description
       "This module contains a collection of YANG type definitions for
        SYSLOG.

        Copyright (c) 2016 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 key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
        NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and
        'OPTIONAL' in the module text are to be interpreted as described
        in RFC 2119 (http://tools.ietf.org/html/rfc2119).

        This version of this YANG module is part of RFC XXXX
        (http://tools.ietf.org/html/rfcXXXX); see the RFC itself for
        full legal notices.";

     reference
       "RFC 5424: The Syslog Protocol";

     revision 2016-11-13 2017-02-14 {
       description
         "Initial Revision";
       reference
         "RFC XXXX: SYSLOG YANG Model";

     }

     typedef severity {
       type enumeration {
         enum "emergency" {
           value 0;
           description
             "The severity level 'Emergency' indicating that the system
              is unusable.";
         }
         enum "alert" {
           value 1;
           description
             "The severity level 'Alert' indicating that an action must be
              taken immediately.";
         }
         enum "critical" {
           value 2;
           description
             "The severity level 'Critical' indicating a critical condition.";
         }
         enum "error" {
           value 3;
           description
             "The severity level 'Error' indicating an error condition.";
         }
         enum "warning" {
           value 4;
           description
             "The severity level 'Warning' indicating a warning condition.";
         }
         enum "notice" {
           value 5;
           description
             "The severity level 'Notice' indicating a normal but significant
              condition.";
         }
         enum "info" {
           value 6;
           description
             "The severity level 'Info' indicating an informational message.";
         }
         enum "debug" {
           value 7;
           description
             "The severity level 'Debug' indicating a debug-level message.";
         }
       }
       description
         "The definitions for Syslog message severity as per RFC 5424.";
     }

     identity syslog-facility {
       description
         "This identity is used as a base for all syslog facilities as
          per RFC 5424.";
     }

     identity kern {
       base syslog-facility;
       description
         "The facility for kernel messages (0) as defined in RFC 5424.";
     }

     identity user {
       base syslog-facility;
       description
         "The facility for user-level messages (1) as defined in RFC 5424.";
     }

     identity mail {
       base syslog-facility;
       description
         "The facility for the mail system (2) as defined in RFC 5424.";
     }

     identity daemon {
       base syslog-facility;
       description
         "The facility for the system daemons (3) as defined in RFC 5424.";
      }

     identity auth {
       base syslog-facility;
       description
         "The facility for security/authorization messages (4) as defined
          in RFC 5424.";
     }

     identity syslog {
       base syslog-facility;
       description
         "The facility for messages generated internally by syslogd
          facility (5) as defined in RFC 5424.";
     }

     identity lpr {
       base syslog-facility;
       description
         "The facility for the line printer subsystem (6) as defined in
          RFC 5424.";
     }

     identity news {
       base syslog-facility;
       description
         "The facility for the network news subsystem (7) as defined in
          RFC 5424.";

     }

     identity uucp {
       base syslog-facility;
       description
         "The facility for the UUCP subsystem (8) as defined in RFC 5424.";
     }

     identity cron {
       base syslog-facility;
       description
         "The facility for the clock daemon (9) as defined in RFC 5424.";
     }

     identity authpriv {
       base syslog-facility;
       description
         "The facility for privileged security/authorization messages (10)
          as defined in RFC 5424.";
     }

     identity ftp {
       base syslog-facility;
       description
         "The facility for the FTP daemon (11) as defined in RFC 5424.";
     }

     identity ntp {
       base syslog-facility;
       description
         "The facility for the NTP subsystem (12) as defined in RFC 5424.";
     }

     identity audit {
       base syslog-facility;
       description
         "The facility for log audit messages (13) as defined in RFC 5424.";
     }

     identity console {
       base syslog-facility;
       description
         "The facility for log alert messages (14) as defined in RFC 5424.";
     }

     identity cron2 {
       base syslog-facility;
       description
         "The facility for the second clock daemon (15) as defined in
          RFC 5424.";
     }

     identity local0 {
       base syslog-facility;
       description
         "The facility for local use 0 messages (16) as defined in
          RFC 5424.";
     }

     identity local1 {
       base syslog-facility;
       description
         "The facility for local use 1 messages (17) as defined in
          RFC 5424.";
     }

     identity local2 {
       base syslog-facility;
       description
         "The facility for local use 2 messages (18) as defined in
          RFC 5424.";
     }

     identity local3 {
       base syslog-facility;
       description
         "The facility for local use 3 messages (19) as defined in
          RFC 5424.";
     }

     identity local4 {
       base syslog-facility;
       description
         "The facility for local use 4 messages (20) as defined in
          RFC 5424.";
     }

     identity local5 {
       base syslog-facility;
       description
         "The facility for local use 5 messages (21) as defined in
          RFC 5424.";
     }

     identity local6 {
       base syslog-facility;
       description
         "The facility for local use 6 messages (22) as defined in
          RFC 5424.";
     }

     identity local7 {
       base syslog-facility;
       description
         "The facility for local use 7 messages (23) as defined in
          RFC 5424.";
     }
   }
   <CODE ENDS>

   Figure 3. ietf-syslog-types Module

4.2.  The ietf-syslog Module

   This module imports typedefs from [RFC6021] and [RFC7223], and it
   references [RFC5424], [RFC5425], [RFC5426], [RFC6587], and [RFC5848].

   <CODE BEGINS> file "ietf-syslog.yang"
   module ietf-syslog {
     namespace "urn:ietf:params:xml:ns:yang:ietf-syslog";
     prefix syslog;

     import ietf-inet-types {
       prefix inet;
     }

     import ietf-interfaces {
       prefix if;
     }

     import ietf-syslog-types {
       prefix syslogtypes;
     }

     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: Lou Berger
                  <mailto:lberger@labn.net>

        WG Chair: Kent Watsen
                  <mailto:kwatsen@juniper.net>

        Editor:   Kiran Agrahara Sreenivasa
                  <mailto:kkoushik@cisco.com>

        Editor:   Clyde Wildes
                  <mailto:cwildes@cisco.com>";
     description
       "This module contains a collection of YANG definitions
        for syslog configuration.

        Copyright (c) 2016 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 key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
        NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and
        'OPTIONAL' in the module text are to be interpreted as described
        in RFC 2119 (http://tools.ietf.org/html/rfc2119).

        This version of this YANG module is part of RFC XXXX
        (http://tools.ietf.org/html/rfcXXXX); see the RFC itself for
        full legal notices.";

     reference
       "RFC 5424: The Syslog Protocol
        RFC 5426: Transmission of Syslog Messages over UDP
        RFC 6587: Transmission of Syslog Messages over TCP
        RFC 5848: Signed Syslog Messages";

     revision 2016-11-13 2017-02-14 {
       description
         "Initial Revision";
       reference
         "RFC XXXX: Syslog YANG Model";
     }

     feature buffer-action console-action {
       description
         "This feature indicates that the local memory logging buffer console action is
          supported.";
     }

     feature buffer-limit-bytes {
    description
      "This feature indicates that the local memory logging buffer
       is limited in size using a limit expressed in bytes.";
  }

  feature buffer-limit-messages file-action {
       description
         "This feature indicates that the local memory logging buffer file action is limited in size using a limit expressed in number of log
       messages.";
          supported.";
     }

     feature file-limit-size {
       description
         "This feature indicates that file logging resources
          are managed using size and number limits.";
     }

     feature file-limit-duration {
       description
         "This feature indicates that file logging resources
          are managed using time based limits.";
     }

     feature select-sev-compare remote-action {
       description
         "This feature indicates that the remote server action is
          supported.";
     }

     feature remote-source-interface {
       description
         "This feature indicates that source-interface is supported
          supported for the remote-action.";
     }

     feature select-adv-compare {
       description
         "This feature represents the ability to select messages
          using the additional comparison operators equal to, or not equal to when comparing
          the syslog message severity.";
     }

     feature select-match {
       description
         "This feature represents the ability to select messages based
          on a Posix 1003.2 regular expression pattern match.";
     }

     feature structured-data {
       description
         "This feature represents the ability to log messages
          in structured-data format as per RFC 5424.";
     }

     feature signed-messages {
       description
         "This feature represents the ability to configure signed
          syslog messages according to RFC 5848.";
     }

     grouping log-severity severity-filter {
       description
         "This grouping defines the severity value that is processing used to select
          log messages."; messages by comparing syslog message severity using
          the following processing rules:
           - if 'none', do not match.
           - if 'all', match.
           - else compare message severity with the specified severity
             according to the default compare rule (all messages of the
             specified severity and greater match) or if the
             select-adv-compare feature is present, the advance-compare
             rule.";
       leaf severity {
         type union {
           type syslogtypes:severity;
           type enumeration {
             enum none {
               value -2;
               description
                 "This enum describes the case where no severities
                  are selected.";
             }
             enum all {
               value -1;
               description
                 "This enum describes the case where all severities
                  are selected.";
             }
           }
         }
         mandatory true;
         description
           "This leaf specifies the syslog message severity. When
         severity is specified, the default severity comparison
         is all messages of the specified severity and greater are
         selected. 'all' is a special case which means all severities
         are selected. 'none' is a special case which means that
         no selection should occur or disable this filter."; severity.";
       }
    leaf compare
       container advanced-compare {
         when '../severity != "all" and
              ../severity != "none"' {
           description
             "The advanced compare leaf container is not applicable for severity
              'all' or severity 'none'";
         }
         if-feature select-sev-compare; select-adv-compare;
         leaf compare {
           type enumeration {
             enum equals-or-higher {
          description
            "This enum specifies all messages of the specified
             severity and higher are logged according to the
             given log-action";
        }
        enum equals {
               description
                 "This enum specifies all messages that are for the specified severity are logged according to the
             given log-action"; comparison operation
                  will be equals.";
             }
             enum not-equals equals-or-higher {
               description
                 "This enum specifies all messages that are not for the specified severity are logged according to the
             given log-action"; comparison operation
                  will be equals or higher.";
             }
           }
           default equals-or-higher;
           description
        "This leaf describes the option
             "The compare can be used to specify how the
         severity comparison is performed.";
    }
  }

  grouping selector {
    description
      "This grouping defines a syslog selector which is operator that
              should be used to
       select log messages for compare the log-action (console, file,
       remote, etc). Choose one of syslog message severity with the following:
         no-facility
         facility [<facility> <severity>...]";
    container selector
              specified severity.";
         }
         leaf action {
      description
        "This container describes the
           type enumeration {
             enum log selector parameters
         for syslog.";
      choice selector-facility {
        mandatory true;
               description
                 "This choice describes enum specifies that if the option to specify no
           facilities, or a specific facility which can compare operation is true
                  the message will be
           all for all facilities.";
        case facility logged.";
              }
             enum block {
               description
                 "This case enum specifies no facilities that if the compare operation is true
                  the message will match when
             comparing not be logged.";
             }
           }
           default log;
           description
             "The action can be used to spectify if the syslog message facility. This is a
             method should be
              logged or blocked based on the outcome of the compare operation.";
         }
         description
           "This leaf describes additional severity compare operations that can
            be used to effectively disable a
             particular log-action (buffer, file, etc)."; in place of the default severity comparison. The compare leaf no-facilities {
            specifies the type empty;
            description
            "This of the compare that is done and the action leaf
            specifies the intended result. Example: compare->equals and action->
            no-match means messages that no facilities are selected
             for this log-action."; have a severity that is not equal to the
            specified severity will be logged.";
       }
     }
        case name

     grouping selector {
       description
         "This case specifies grouping defines a syslog selector which is used to
          select log messages for the log-action (console, file,
          remote, etc.). Choose one or more specified facilities
             will match when comparing both of the syslog following:
            facility [<facility> <severity>...]
            pattern-match regular-expression-match-string
          If both facility and pattern-match are specified, both must
          match in order for a log message facility."; to be selected.";
       container selector {
         description
           "This container describes the log selector parameters
            for syslog.";
         list facility-list {
           key facility; "facility severity";
           ordered-by user;
           description
             "This list describes a collection of syslog
              facilities and severities.";
           leaf facility {
             type union {
               type identityref {
                 base syslogtypes:syslog-facility;
               }
               type enumeration {
                 enum all {
                   description
                     "This enum describes the case where all
                      facilities are requested.";
                 }
               }
             }
             description
               "The leaf uniquely identifies a syslog facility.";
           }
           uses log-severity;
          }
        } severity-filter;
         }
         leaf pattern-match {
           if-feature select-match;
           type string;
           description
             "This leaf desribes describes a Posix 1003.2 regular expression
              string that can be used to select a syslog message for
              logging. The match is performed on the RFC 5424
              SYSLOG-MSG field.";
         }
       }
     }
     grouping structured-data {
       description
         "This grouping defines the syslog structured data option
          which is used to select the format used to write log
          messages.";
       leaf structured-data {
         if-feature structured-data;
         type boolean;
         default false;
         description
           "This leaf describes how log messages are written.
            If true, messages will be written with one or more
            STRUCTURED-DATA elements as per RFC5424; if false,
            messages will be written with STRUCTURED-DATA =
            NILVALUE.";
       }
     }

     container syslog {
       presence "Enables logging.";
       description
         "This container describes the configuration parameters for
          syslog.";
       container actions {
         description
           "This container describes the log-action parameters
            for syslog.";
         container console {
           if-feature console-action;
           presence "Enables logging console configuration"; to the console";
           description
             "This container describes the configuration parameters for
              console logging.";
           uses selector;
         }
         container buffer {
        if-feature buffer-action;
        description
          "This container describes the configuration parameters for
           local memory buffer logging. The buffer is circular in
           nature, so newer messages overwrite older messages after
           the buffer is filled. The method used to read syslog messages
           from the buffer is supplied by the local implementation.";
        uses selector;
        uses structured-data;
        leaf buffer-limit-bytes {
          if-feature buffer-limit-bytes;
          type uint64;
          units "bytes";
          description
            "This leaf configures the amount of memory (in bytes) that
             will be dedicated to the local memory logging buffer.

             The default value varies by implementation.";
        }
        leaf buffer-limit-messages {
          if-feature buffer-limit-messages;
          type uint64;
          units "log messages";
          description
            "This leaf configures the number of log messages that
             will be dedicated to the local memory logging buffer.
             The default value varies by implementation.";
        }
      }
      container file {
           if-feature file-action;
           description
             "This container describes the configuration parameters for
              file logging. If file-archive limits are not supplied, it
              is assumed that the local implementation defined limits will
              be used.";
           list log-file {
             key "name";
             description
               "This list describes a collection of local logging
                files.";
             leaf name {
               type inet:uri {
                 pattern 'file:.*';
               }
               description
                 "This leaf specifies the name of the log file which
                  MUST use the uri scheme file:.";

             }
             uses selector;
             uses structured-data;
             container file-rotation {
               description
                 "This container describes the configuration
                  parameters for log file rotation.";
               leaf number-of-files {
                 if-feature file-limit-size;
                 type uint32;
                 default 1;
                 description
                   "This leaf specifies the maximum number of log
                    files retained. Specify 1 for implementations
                    that only support one log file.";
               }
               leaf max-file-size {
                 if-feature file-limit-size;
                 type uint64; uint32;
                 units "megabytes";
                 description
                   "This leaf specifies the maximum log file size.";
               }
               leaf rollover {
                 if-feature file-limit-duration;
                 type uint32;
                 units "minutes";
                 description
                   "This leaf specifies the length of time that log
                    events should be written to a specific log file.
                    Log events that arrive after the rollover period
                    cause the current log file to be closed and a new
                    log file to be opened.";
               }
               leaf retention {
                 if-feature file-limit-duration;
                 type uint16; uint32;
                 units "hours";
                 description
                   "This leaf specifies the length of time that
                    completed/closed log event files should be stored
                    in the file system before they are deleted.";
               }
             }
           }
         }
         container remote {
           if-feature remote-action;
           description
             "This container describes the configuration parameters for
              forwarding syslog messages to remote relays or collectors.";
           list destination {
             key "name";
             description
               "This list describes a collection of remote logging
                destinations.";
             leaf name {
               type string;
               description
                 "An arbitrary name for the endpoint to connect to.";
             }
             choice transport {
               mandatory true;
               description
                 "This choice describes the transport option.";
               case tcp {
                 container tcp {
                   description
                     "This container describes the TCP transport
                      options.";
                   reference
                     "RFC 6587: Transmission of Syslog Messages over TCP";
                   leaf address {
                     type inet:host;
                     description
                       "The leaf uniquely specifies the address of
                        the remote host. One of the following must
                        be specified: an ipv4 address, an ipv6
                        address, or a host name.";
                   }
                   leaf port {
                     type inet:port-number;
                     default 514;
                     description
                       "This leaf specifies the port number used to
                        deliver messages to the remote server.";
                   }
                 }
               }
               case udp {
                 container udp {
                   description
                     "This container describes the UDP transport
                      options.";
                   reference
                     "RFC 5426: Transmission of Syslog Messages over UDP";
                   leaf address {
                     type inet:host;
                     description
                       "The leaf uniquely specifies the address of
                        the remote host. One of the following must be
                        specified: an ipv4 address, an ipv6 address,
                        or a host name.";
                   }
                   leaf port {
                     type inet:port-number;
                     default 514;
                     description
                       "This leaf specifies the port number used to
                        deliver messages to the remote server.";
                   }
                 }
               }
             }
             uses selector;
             uses structured-data;
             leaf facility-override {
               type identityref {
                 base syslogtypes:syslog-facility;
               }
               description
                 "If specified, this leaf specifies the facility used
                  to override the facility in messages delivered to the
                  remote server.";
             }
             leaf source-interface {
               if-feature remote-source-interface;
               type if:interface-ref;
               description
                 "This leaf sets the source interface to be used to send
                  message to the remote syslog server. If not set,
                  messages sent to a remote syslog server will
                  contain the IP address of the interface the syslog
                  message uses to exit the network element";
             }
             container signing-options {
               if-feature signed-messages;
               presence
                 "If present, syslog-signing options is activated.";
               description
                 "This container describes the configuration
                  parameters for signed syslog messages as described
                  by RFC 5848.";
               reference
                 "RFC 5848: Signed Syslog Messages";
               leaf cert-initial-repeat {
                 type uint16;
                 mandatory true;
                 description
                 "This leaf specifies the number of times each
                  Certificate Block should be sent before the first
                  message is sent.";
               }
               leaf cert-resend-delay {
                 type uint16;
                 units "seconds";
                 mandatory true;
                 description
                   "This leaf specifies the maximum time delay in
                    seconds until resending the Certificate Block.";
               }
               leaf cert-resend-count {
                 type uint16;
                 mandatory true;
                 description
                   "This leaf specifies the maximum number of other
                    syslog messages to send until resending the
                    Certificate Block.";
               }
               leaf max-delay {
                 type uint16;
                 units "seconds";
                 mandatory true;
                 description
                   "This leaf specifies when to generate a new
                    Signature Block. If this many seconds have
                    elapsed since the message with the first message
                    number of the Signature Block was sent, a new
                    Signature Block should be generated.";
               }
               leaf number-resends {
                 type uint16;
                 mandatory true;
                 description
                   "This leaf specifies the number of times a
                    Signature Block is resent. (It is recommended to
                    select a value of greater than 0 in particular
                    when the UDP transport [RFC5426] is used.).";
               }
               leaf resend-delay {
                 type uint16;
                 units "seconds";
                 mandatory true;
                 description
                   "This leaf specifies when to send the next
                    Signature Block transmission based on time. If
                    this many seconds have elapsed since the previous
                    sending of this Signature Block, resend it.";
               }
               leaf resend-count {
                 type uint16;
                 mandatory true;
                 description
                   "This leaf specifies when to send the next
                    Signature Block transmission based on a count.
                    If this many other syslog messages have been sent
                    since the previous sending of this Signature
                    Block, resend it.";
               }
             }
           }
         }
      container session {
        description
          "This container describes the configuration parameters for
           user CLI session logging configuration.";
        container all-users {
          presence "Enables logging to all user sessions.";
          description
            "This container describes the configuration
             parameters for all users.";
          uses selector;
        }
        list user {
          key "name";
          description
            "This list describes a collection of user names.";
          leaf name {
            type string;
            description
              "This leaf uniquely describes a user name which
               is the login name of the user whose session
               is to receive log messages.";
          }
          uses selector;
        }
      }
       }
     }
   }
   <CODE ENDS>
   Figure 4. ietf-syslog Module

5.  Usage Examples

      Requirement:
      Enable console logging of syslogs of severity critical

      Here is the example syslog configuration xml:
      <config xmlns:xc="urn:ietf:params:xml:ns:netconf:base:1.0">
        <syslog xmlns="urn:ietf:params:xml:ns:yang:ietf-syslog"
                xmlns:syslog="urn:ietf:params:xml:ns:yang:ietf-syslog">
          <actions>
            <console>
              <selector>
                <facility-list>
                  <facility>all</facility>
                  <severity>critical</severity>
             </facility>
                </facility-list>
              </selector>
            </console>
          </actions>
        </syslog>
      </config>

      Enable remote logging of syslogs to udp destination 2001:db8:a0b:12f0::1
      for facility auth, severity error

      <config xmlns:xc="urn:ietf:params:xml:ns:netconf:base:1.0">
        <syslog xmlns="urn:ietf:params:xml:ns:yang:ietf-syslog"
                xmlns:syslog="urn:ietf:params:xml:ns:yang:ietf-syslog">
          <actions>
            <remote>
              <destination>
                <name>remote1</name>
                <udp>
                  <address>2001:db8:a0b:12f0::1</address>
                </udp>
                <selector>
                  <facility-list>
                    <facility xmlns:syslogtypes=
                      "urn:ietf:params:xml:ns:yang:ietf-syslog-types">
                      syslogtypes:auth</facility>
                    <severity>error</severity>
               <facility>
             <selector>
                  </facility-list>
                </selector>
              </destination>
            </remote>
          </actions>
        </syslog>
      </config>

   Figure 5. ietf-syslog Examples

6.  Acknowledgements

   The authors wish to thank the following who commented on this
   proposal:

      Andy Bierman
      Martin Bjorklund
      Alex Campbell
      Jim Gibson
      Jeffrey Haas
      John Heasley
      Giles Heron
      Lisa Huang
      Mahesh Jethanandani
      Jeffrey K Lange
      Jan Lindblad
      Chris Lonvick
      Tom Petch
      Juergen Schoenwaelder
      Phil Shafer
      Jason Sterne
      Peter Van Horne
      Bert Wijnen
      Aleksandr Zhdankin

7.  IANA Considerations

   This document registers two URIs in the IETF XML registry [RFC3688].

   Following the format in RFC 3688, the following registration is
   requested to be made:

   URI: urn:ietf:params:xml:ns:yang:ietf-syslog-types

   Registrant Contact: The IESG.

   XML: N/A, the requested URI is an XML namespace.

   This document registers a YANG module in the YANG Module Names
   registry [RFC6020].

   name: ietf-syslog-types namespace: urn:ietf:params:xml:ns:yang:ietf-
   syslog-types

   prefix: ietf-syslog-types reference: RFC XXXX

   Following the format in RFC 3688, the following registration is
   requested to be made:

   URI: urn:ietf:params:xml:ns:yang:ietf-syslog

   Registrant Contact: The IESG.

   XML: N/A, the requested URI is an XML namespace.

   This document registers a YANG module in the YANG Module Names
   registry [RFC6020].

   name: ietf-syslog namespace: urn:ietf:params:xml:ns:yang:ietf-syslog

   prefix: ietf-syslog

   reference: RFC XXXX

8.  Security Considerations

   The YANG module defined in this memo is 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 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.

8.1.  Resource Constraints

   Network administrators must take the time to estimate the appropriate
   memory limits caused by the configuration of actions/buffer using
   buffer-limit-bytes and/or buffer-limit-messages where necessary to
   limit the amount of memory used.

   Network administrators must take the time to estimate the appropriate
   storage capacity caused by the configuration of actions/file using
   file-archive attributes to limit storage used.

   It is the responsibility of the network administrator to ensure that
   the configured message flow does not overwhelm system resources.

8.2.  Inappropriate Configuration

   It is the responsibility of the network admisintrator administrator to ensure that
   the messages are actually going to the intended recipients.

9.  References

9.1.  Normative References

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

   [RFC5424]  Gerhards, R., "The Syslog Protocol", RFC 5424, DOI
              10.17487/RFC5424, March 2009,
              <http://www.rfc-editor.org/info/rfc5424>. <http://www.rfc-editor.org/
              info/rfc5424>.

   [RFC5426]  Okmianski, A., "Transmission of Syslog Messages over UDP",
              RFC 5426, DOI 10.17487/RFC5426, March 2009,
              <http://www.rfc-editor.org/info/rfc5426>. <http://www
              .rfc-editor.org/info/rfc5426>.

   [RFC5848]  Kelsey, J., Callas, J., J. and A. Clemm, "Signed Syslog
              Messages", RFC 5848, DOI 10.17487/RFC5848, May 2010,
              <http://www.rfc-editor.org/info/rfc5848>.

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

   [RFC6021]  Schoenwaelder, J., Ed., "Common YANG Data Types", RFC
              6021, DOI 10.17487/RFC6021, October 2010,
              <http://www.rfc-editor.org/info/rfc6021>. <http://www.rfc-
              editor.org/info/rfc6021>.

   [RFC6587]  Gerhards, R. and C. Lonvick, "Transmission of Syslog
              Messages over TCP", RFC 6587, DOI 10.17487/RFC6587, April
              2012, <http://www.rfc-editor.org/info/rfc6587>.

   [RFC7223]  Bjorklund, M., "A YANG Data Model for Interface
              Management", RFC 7223, DOI 10.17487/RFC7223, May 2014,
              <http://www.rfc-editor.org/info/rfc7223>.

9.2.  Informative References

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

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

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <http://www.rfc-editor.org/info/rfc6242>.

Appendix A.  Implementor Guidelines

Appendix A.1.  Extending Facilities
   Many vendors extend the list of facilities available for logging in
   their implementation.  Additional facilities may not work with the
   syslog protocol as defined in [RFC5424] and hence such facilities
   apply for local syslog-like logging functionality.

   The following is an example that shows how additional facilities
   could be added to the list of available facilities (in this example
   two facilities are added):

   module vendor-syslog-types-example {
     namespace "urn:vendor:params:xml:ns:yang:vendor-syslog-types";
     prefix vendor-syslogtypes;

     import ietf-syslog-types {
       prefix syslogtypes;
     }

     organization "Example, Inc.";
     contact
       "Example, Inc.
        Customer Service

        E-mail: syslog-yang@example.com";

     description
       "This module contains a collection of vendor-specific YANG type
        definitions for SYSLOG.";

     revision 2016-11-13 {
       description
         "Version 1.0";
       reference
         "Vendor SYSLOG Types: SYSLOG YANG Model";
     }

     identity vendor_specific_type_1 {
       base syslogtypes:syslog-facility;
     }

     identity vendor_specific_type_2 {
       base syslogtypes:syslog-facility;
     }
   }

Authors' Addresses
   Clyde Wildes (editor) Wildes, editor
   Cisco Systems Inc.
   170 West Tasman Drive
   San Jose, CA 95134
   US

   Phone: +1 408 527-2672
   Email: cwildes@cisco.com

   Kiran Koushik (editor) Koushik, editor
   Cisco Systems Inc.
   12515Research Blvd., Building 4
   Austin, TX 78759
   US

   Phone: +1 512 378-1482
   Email: kkoushik@cisco.com