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A YANG Data Model for Syslog Configuration
draft-ietf-netmod-syslog-model-33

Document Type Active Internet-Draft (netmod WG)
Authors Joe Clarke , Mahesh Jethanandani , Clyde Wildes , Kiran Koushik
Last updated 2024-10-02 (Latest revision 2024-09-18)
Replaces draft-wildes-netmod-syslog-model
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draft-ietf-netmod-syslog-model-33
NETMOD WG                                                 J. Clarke, Ed.
Internet-Draft                                                     Cisco
Intended status: Standards Track                    M. Jethanandani, Ed.
Expires: 22 March 2025                                    Kloud Services
                                                          C. Wildes, Ed.
                                                      Cisco Systems Inc.
                                                         K. Koushik, Ed.
                                                        Verizon Wireless
                                                       18 September 2024

               A YANG Data Model for Syslog Configuration
                   draft-ietf-netmod-syslog-model-33

Abstract

   This document defines a YANG data model for the configuration of a
   syslog process.  It is intended that this model be used by vendors
   who implement syslog collectors in their systems.

Status of This Memo

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

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

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

   This Internet-Draft will expire on 22 March 2025.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  NMDA Compliance . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Editorial Note (To be removed by RFC Editor)  . . . . . . . .   4
   5.  Design of the Syslog Model  . . . . . . . . . . . . . . . . .   4
     5.1.  Syslog Module . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Syslog YANG Module  . . . . . . . . . . . . . . . . . . . . .   9
     6.1.  The ietf-syslog Module  . . . . . . . . . . . . . . . . .   9
   7.  Usage Examples  . . . . . . . . . . . . . . . . . . . . . . .  29
     7.1.  Syslog Configuration for Severity Critical  . . . . . . .  29
     7.2.  Remote Syslog Configuration . . . . . . . . . . . . . . .  30
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  31
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  31
     9.1.  The IETF XML Registry . . . . . . . . . . . . . . . . . .  32
     9.2.  The YANG Module Names Registry  . . . . . . . . . . . . .  32
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  32
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  33
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  33
     11.2.  Informative References . . . . . . . . . . . . . . . . .  36
   Appendix A.  Tree Diagrams  . . . . . . . . . . . . . . . . . . .  36
     A.1.  Complete Tree Diagram . . . . . . . . . . . . . . . . . .  36
   Appendix B.  Implementer Guidelines . . . . . . . . . . . . . . .  48
     B.1.  Extending Facilities  . . . . . . . . . . . . . . . . . .  48
     B.2.  Syslog Terminal Output  . . . . . . . . . . . . . . . . .  49
     B.3.  Syslog File Naming Convention . . . . . . . . . . . . . .  50
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  50

1.  Introduction

   This document defines a YANG [RFC7950] 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.

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   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 syslog collector.

   Essentially, a syslog process receives messages (from the kernel,
   processes, applications or other syslog processes) and processes
   them.  The processing may involve logging to a local file, and/or
   displaying on console, 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.

   Such definitions of syslog protocol are defined in [RFC5424] , and
   are used in this RFC.

   The YANG model in this document conforms to the Network Management
   Datastore Architecture defined in [RFC8342].

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Terminology

   The following terms are used throughout this document:

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

   *  Relay: A "relay" is an entity that forwards syslog messages.  It
      accepts messages from originators or other relays and sends them
      to collectors or other relays.  The term is defined in [RFC5424]

   *  Collector: A "collector" gathers syslog content for further
      analysis.  The term is defined in [RFC5424].

   *  Action: The term "action" refers to the processing that takes
      place for each syslog message received.

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3.  NMDA Compliance

   The YANG model in this document conforms to the Network Management
   Datastore Architecture defined in [RFC8342] .

4.  Editorial Note (To be removed by RFC Editor)

   This document contains many placeholder values that need to be
   replaced with finalized values at the time of publication.  This note
   summarizes all of the substitutions that are needed.  No other RFC
   Editor instructions are specified elsewhere in this document.

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

   *  I-D.ietf-netconf-crypto-types --> the assigned RFC value for
      draft-ietf-netconf-crypto-types

   *  I-D.ietf-netconf-tls-client-server --> the assigned RFC value for
      draft-ietf-netconf-tls-client-server

   *  zzzz --> the assigned RFC value for this draft

5.  Design of the Syslog Model

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

   The module defines leafs that are common across implementations.  Its
   simple design is meant to offer maximum flexibility.  However, not
   all optional features defined in this document are present in all
   vendor implementations.  Vendors therefore, need to use the feature
   statements to specify the optional features they support.  At the
   same time, vendors can augment the model to add proprietary features.
   Extending Facilities (Appendix B.1) shows an examples of how that can
   be realized.

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

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

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

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

   Figure 1.  Syslog Processing Flow

   Collectors are configured using the leaves in the syslog model
   "actions" container which correspond to each message collector:

      console

      log file(s)

      remote relay(s)/collector(s)

   Within each action, a selector is used to filter syslog messages.  A
   selector consists of a list of one or more filters specified by
   facility-severity pairs, and, if supported via the select-match
   feature, an optional regular expression pattern match that is
   performed on the [RFC5424] field.

   A syslog message is processed if:

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          There is an element of facility-list (F, S) where
              the message facility matches F
              and the message severity matches S
          and/or the message text matches the regex pattern (if it
              is present)

   The facility is one of a specific syslog-facility, or all facilities.

   The model offers the ability to select a transport that a user might
   want to use for a remote relay or collector.  The choice is between
   using UDP, or TLS based sessions.  The user can configure multiple
   relays or collectors, but they have to use the same transport.

   The severity is one of type syslog-severity, all severities, or none.
   None is a special case that can be used to disable a filter.  When
   filtering severity, the default comparison is that messages of the
   specified severity and higher are selected to be logged.  This is
   shown in the model as "default equals-or-higher".  This behavior can
   be altered if the select-adv-compare feature is enabled to specify a
   compare operation and an action.  Compare operations are: "equals" to
   select messages with this single severity, or "equals-or-higher" to
   select messages of the specified severity and higher.  Actions are
   used to log the message, block the message, or stop the message from
   being logged.

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

5.1.  Syslog Module

   A simplified tree representation of the data model is used in this
   document.  Please see [RFC8340] for tree diagram notation.

 module: ietf-syslog
   +--rw syslog!
      +--rw actions
         +--rw console! {console-action}?
         |  +--rw filter
         |  |  +--rw facility-list* [facility severity]
         |  |     +--rw facility            union
         |  |     +--rw severity            union
         |  |     +--rw advanced-compare {select-adv-compare}?
         |  |        +--rw compare?   enumeration
         |  |        +--rw action?    identityref
         |  +--rw pattern-match?   string {select-match}?
         +--rw file {file-action}?
         |  +--rw log-file* [name]

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         |     +--rw name               inet:uri
         |     +--rw filter
         |     |  +--rw facility-list* [facility severity]
         |     |     +--rw facility            union
         |     |     +--rw severity            union
         |     |     +--rw advanced-compare {select-adv-compare}?
         |     |        +--rw compare?   enumeration
         |     |        +--rw action?    identityref
         |     +--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?     uint32 {file-limit-size}?
         |        +--rw rollover?          uint32
         |        |       {file-limit-duration}?
         |        +--rw retention?         uint32
         |                {file-limit-duration}?
         +--rw remote {remote-action}?
            +--rw destination* [name]
               +--rw name                 string
               +--rw (transport)
               |  +--:(udp)
               |  |  +--rw udp
               |  |     +--rw udp* [address]
               |  |        +--rw address    inet:host
               |  |        +--rw port?      inet:port-number
               |  +--:(tls)
               |     +--rw tls
               |        +--rw tls* [address]
               |           +--rw address                  inet:host
               |           +--rw port?
               |           |       inet:port-number
               |           +--rw client-identity!
               |           |  +--rw (auth-type)
               |           |        ...
               |           +--rw server-authentication
               |           |  +--rw ca-certs! {server-auth-x509-cert}?
               |           |  |     ...
               |           |  +--rw ee-certs! {server-auth-x509-cert}?
               |           |  |     ...
               |           |  +--rw raw-public-keys!
               |           |  |       {server-auth-raw-public-key}?
               |           |  |     ...
               |           |  +--rw tls12-psks?        empty
               |           |  |       {server-auth-tls12-psk}?
               |           |  +--rw tls13-epsks?       empty
               |           |          {server-auth-tls13-epsk}?
               |           +--rw hello-params {tlscmn:hello-params}?

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               |           |  +--rw tls-versions
               |           |  |     ...
               |           |  +--rw cipher-suites
               |           |        ...
               |           +--rw keepalives {tls-client-keepalives}?
               |              +--rw peer-allowed-to-send?   empty
               |              +--rw test-peer-aliveness!
               |                    ...
               +--rw filter
               |  +--rw facility-list* [facility severity]
               |     +--rw facility            union
               |     +--rw severity            union
               |     +--rw advanced-compare {select-adv-compare}?
               |        +--rw compare?   enumeration
               |        +--rw action?    identityref
               +--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! {signed-messages}?
                  +--rw cert-signers
                     +--rw cert-signer* [name]
                     |  +--rw name              string
                     |  +--rw cert
                     |  |  +--rw public-key-format?
                     |  |  |       identityref
                     |  |  +--rw public-key?                    binary
                     |  |  +--rw private-key-format?
                     |  |  |       identityref
                     |  |  +--rw (private-key-type)
                     |  |  |  +--:(cleartext-private-key)
                     |  |  |  |        {cleartext-private-keys}?
                     |  |  |  |     ...
                     |  |  |  +--:(hidden-private-key)
                     |  |  |  |        {hidden-private-keys}?
                     |  |  |  |     ...
                     |  |  |  +--:(encrypted-private-key)
                     |  |  |           {encrypted-private-keys}?
                     |  |  |        ...
                     |  |  +--rw cert-data?
                     |  |  |       end-entity-cert-cms
                     |  |  +---n certificate-expiration
                     |  |  |       {certificate-expiration-notification}
 ?
                     |  |  |  +-- expiration-date
                     |  |  |          yang:date-and-time
                     |  |  +---x generate-csr {csr-generation}?

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                     |  |     +---w input
                     |  |     |     ...
                     |  |     +--ro output
                     |  |           ...
                     |  +--rw hash-algorithm?   enumeration
                     +--rw cert-initial-repeat?   uint32
                     +--rw cert-resend-delay?     uint32
                     +--rw cert-resend-count?     uint32
                     +--rw sig-max-delay?         uint32
                     +--rw sig-number-resends?    uint32
                     +--rw sig-resend-delay?      uint32
                     +--rw sig-resend-count?      uint32

                Figure 1: Tree Diagram for Syslog Model

6.  Syslog YANG Module

6.1.  The ietf-syslog Module

   This module imports typedefs from [RFC6991], [RFC8343], groupings
   from [I-D.ietf-netconf-crypto-types], and
   [I-D.ietf-netconf-tls-client-server], and it references [RFC5424],
   [RFC5425], [RFC5426], [RFC5848], [RFC8089], [RFC8174], and
   [Std-1003.1-2008].

   <CODE BEGINS> file "ietf-syslog@2024-09-18.yang"
   module ietf-syslog {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-syslog";
     prefix syslog;

     import ietf-inet-types {
       prefix inet;
       reference
         "RFC 6991: Common YANG Data Types";
     }

     import ietf-interfaces {
       prefix if;
       reference
         "RFC 8343: A YANG Data Model for Interface Management";
     }

     import ietf-tls-client {
       prefix tlsc;
       reference

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         "I-D.ietf-netconf-tls-client-server:
       YANG Groupings for TLS Clients and TLS Servers";
     }

     import ietf-crypto-types {
       prefix ct;
       reference
         "I-D.ietf-netconf-crypto-types: YANG Data Types for
         Cryptography";
     }

     organization
       "IETF NETMOD (Network Modeling) Working Group";
     contact
       "WG Web:   <https://datatracker.ietf.org/wg/netmod/>
        WG List:  <mailto:netmod@ietf.org>

        Editor:   Mahesh Jethanandani
        <mailto:mjethanandani@gmail.com>

        Editor:   Joe Clarke
        <mailto:jclarke@cisco.com>

        Editor:   Kiran Agrahara Sreenivasa
        <mailto:kirankoushik.agraharasreenivasa@verizonwireless.com>

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

        Copyright (c) 2024 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 Revised BSD License
        set forth in Section 4.c of the IETF Trust's Legal
        Provisions Relating to IETF Documents
        (https://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC zzzz
        (https://www.rfc-editor.org/info/rfczzzz);
        see the RFC itself for full legal notices.

        The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
        NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',

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       'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
        are to be interpreted as described in BCP 14 (RFC 2119)
        (RFC 8174) when, and only when, they appear in all capitals,
        as shown here.";

     revision 2024-09-18 {
       description
         "Initial Revision";
       reference
         "RFC zzzz: Syslog YANG Model";
     }

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

     feature file-action {
       description
         "This feature indicates that the local file action is
          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 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.";
     }

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     feature select-adv-compare {
       description
         "This feature represents the ability to select messages
          using the additional comparison operators 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.";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     feature signed-messages {
       description
         "This feature represents the ability to configure signed
          syslog messages.";
       reference
         "RFC 5848: Signed Syslog Messages";
     }

     typedef syslog-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

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              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.
          Note that a lower value is a higher severity. Comparisons
          of equal-or-higher severity mean equal or lower numeric
          value";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity syslog-facility {
       description
         "This identity is used as a base for all syslog
          facilities.";
       reference
         "RFC 5424: The Syslog Protocol";

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     }

     identity kern {
       base syslog-facility;
       description
         "The facility for kernel messages (0).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity user {
       base syslog-facility;
       description
         "The facility for user-level messages (1).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity mail {
       base syslog-facility;
       description
         "The facility for the mail system (2).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity daemon {
       base syslog-facility;
       description
         "The facility for the system daemons (3).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity auth {
       base syslog-facility;
       description
         "The facility for security/authorization messages (4).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity syslog {
       base syslog-facility;
       description
         "The facility for messages generated internally by syslogd
                                      facility (5).";
       reference

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         "RFC 5424: The Syslog Protocol";
     }

     identity lpr {
       base syslog-facility;
       description
         "The facility for the line printer subsystem (6).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity news {
       base syslog-facility;
       description
         "The facility for the network news subsystem (7).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity uucp {
       base syslog-facility;
       description
         "The facility for the UUCP subsystem (8).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity cron {
       base syslog-facility;
       description
         "The facility for the clock daemon (9).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity authpriv {
       base syslog-facility;
       description
         "The facility for privileged security/authorization
                                        messages (10).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity ftp {
       base syslog-facility;
       description
         "The facility for the FTP daemon (11).";

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       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity ntp {
       base syslog-facility;
       description
         "The facility for the NTP subsystem (12).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity audit {
       base syslog-facility;
       description
         "The facility for log audit messages (13).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity console {
       base syslog-facility;
       description
         "The facility for log alert messages (14).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity cron2 {
       base syslog-facility;
       description
         "The facility for the second clock daemon (15).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity local0 {
       base syslog-facility;
       description
         "The facility for local use 0 messages (16).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity local1 {
       base syslog-facility;
       description
         "The facility for local use 1 messages (17).";

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       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity local2 {
       base syslog-facility;
       description
         "The facility for local use 2 messages (18).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity local3 {
       base syslog-facility;
       description
         "The facility for local use 3 messages (19).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity local4 {
       base syslog-facility;
       description
         "The facility for local use 4 messages (20).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity local5 {
       base syslog-facility;
       description
         "The facility for local use 5 messages (21).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity local6 {
       base syslog-facility;
       description
         "The facility for local use 6 messages (22).";
       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity local7 {
       base syslog-facility;
       description
         "The facility for local use 7 messages (23).";

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       reference
         "RFC 5424: The Syslog Protocol";
     }

     identity action {
       description
         "Base identity for action for how a message will be
          handled.";
     }

     identity log {
       base action;
       description
         "This identity specifies that if the compare operation is
          true the message will be logged.";
     }

     identity block {
       base action;
       description
         "This identity specifies that if the compare operation is
          true the message will not be logged.";
     }

     identity stop {
       base action;
       description
         "This identity specifies that if the compare operation is
          true the message will not be logged and no further
          processing will occur for it.";
     }

     grouping severity-filter {
       description
         "This grouping defines the processing used to select
          log 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, use
            the advance-compare rule.";

       leaf severity {
         type union {
           type syslog-severity;

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           type enumeration {
             enum none {
               value 2147483647;
               description
                 "This enum describes the case where no
                  severities are selected.";
             }
             enum all {
               value -2147483648;
               description
                 "This enum describes the case where all
                  severities are selected.";
             }
           }
         }
         mandatory true;
         description
           "This leaf specifies the syslog message severity.";
       }

       container advanced-compare {
         when "../severity != \"all\" and
           ../severity != \"none\"" {
           description
             "The advanced compare container is not applicable
              for severity 'all' or severity 'none'";
         }
         if-feature "select-adv-compare";

         leaf compare {
           type enumeration {
             enum equals {
               description
                 "This enum specifies that the severity
                  comparison operation will be equals.";
             }
             enum equals-or-higher {
               description
                 "This enum specifies that the severity
                  comparison operation will be equals or
                  higher.";
             }
           }
           default "equals-or-higher";
           description
             "The compare can be used to specify the comparison
              operator that should be used to compare the syslog
              message severity with the specified severity.";

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         }

         leaf action {
           type identityref {
             base "action";
           }
           default "log";
           description
             "The action can be used to specify how the message
              should be handled. This may include logging the
              message, not logging the message (i.e., blocking
              it), or stopping further processing.";
         }
         description
           "This container describes additional severity compare
            operations that can be used in place of the default
            severity comparison. The compare leaf specifies the
            type of the compare that is done and the action leaf
            specifies the intended result.
            Example: compare->equals and action->block means
            messages that have a severity that are equal to the
            specified severity will not be logged.";
       }
     }

     grouping selector {
       description
         "This grouping defines a syslog selector which is used to
          select log messages for the log-actions (console, file,
          remote, etc.). Choose one or both of the 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 to be selected.";

       container filter {
         description
           "This container describes the syslog filter
            parameters.";

         list facility-list {
           key "facility severity";
           ordered-by user;
           description
             "This list describes a collection of syslog
              facilities and severities.";

           leaf facility {

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             type union {
               type identityref {
                 base 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 severity-filter;
         }
       }

       leaf pattern-match {
         if-feature "select-match";
         type string;
         description
           "This leaf 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 SYSLOG-MSG
            field.";
         reference
           "RFC 5424: The Syslog Protocol
            Std-1003.1-2008 Regular Expressions";
       }
     }

     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; if false, messages will be

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            written with STRUCTURED-DATA = NILVALUE.";
         reference
           "RFC 5424: The Syslog Protocol";
       }
     }

     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 to the console";
           description
             "This container describes the configuration
              parameters for console logging.";
           uses selector;
         }

         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:.*';
               }

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               description
                 "This leaf specifies the name of the log
                  file which MUST use the uri scheme
                  file:.";
               reference
                 "RFC 8089: The file URI Scheme";
             }

             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 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.";
               }

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               leaf retention {
                 if-feature "file-limit-duration";
                 type uint32;
                 units "minutes";
                 description
                   "This leaf specifies the length of time
                    that completed/closed log event files
                    should be stored in the file system
                    before they are removed.";
               }
             }
           }
         }

         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 udp {
                 container udp {
                   description
                     "This container describes the UDP transport
                      options.";
                   reference
                     "RFC 5426: Transmission of Syslog Messages over
                                UDP";

                   list udp {
                     key "address";

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                     description
                       "List of all UDP sessions.";

                     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 tls {
                 container tls {
                   description
                     "This container describes the TLS transport
                      options.";
                   reference
                     "RFC 5425: Transport Layer Security (TLS) Transport
                                Mapping for Syslog ";

                   list tls {
                     key "address";
                     description
                       "List of all TLS based sessions.";

                     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.";
                     }

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                     leaf port {
                       type inet:port-number;
                       default "6514";
                       description
                         "TCP port 6514 has been allocated as the
                          default port for syslog over TLS.";
                     }
                     uses tlsc:tls-client-grouping;
                   }
                 }
               }
             }

             uses selector;
             uses structured-data;

             leaf facility-override {
               type identityref {
                 base 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 messages to the remote syslog server. If not set,
                  messages can be sent on any interface.";
             }

             container signing {
               if-feature "signed-messages";
               presence
                 "If present, syslog-signing options is activated.";
               description
                 "This container describes the configuration
                  parameters for signed syslog messages.";
               reference
                 "RFC 5848: Signed Syslog Messages";

               container cert-signers {
                 description
                   "This container describes the signing certificate

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                    configuration for Signature Group 0 which covers the
                    case for administrators who want all Signature
                    Blocks to be sent to a single destination.";

                 list cert-signer {
                   key "name";
                   description
                     "This list describes a collection of syslog message
                      signers.";

                   leaf name {
                     type string;
                     description
                       "This leaf specifies the name of the syslog
                        message signer.";
                   }

                   container cert {
                     uses ct:asymmetric-key-pair-with-cert-grouping;
                     description
                       "This is the certificate that is periodically
                        sent to the remote receiver. The certificate is
                        inherently associated with its private
                        and public keys.";
                   }

                   leaf hash-algorithm {
                     type enumeration {
                       enum SHA1 {
                         value 1;
                         description
                           "This enum describes the SHA1 algorithm.";
                       }
                       enum SHA256 {
                         value 2;
                         description
                           "This enum describes the SHA256 algorithm.";
                       }
                     }
                     description
                       "This leaf describes the syslog signer hash
                        algorithm used.";
                   }
                 }

                 leaf cert-initial-repeat {
                   type uint32;
                   default "3";

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                   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 uint32;
                   units "seconds";
                   default "3600";
                   description
                     "This leaf specifies the maximum time delay in
                      seconds until resending the Certificate Block.";
                 }

                 leaf cert-resend-count {
                   type uint32;
                   default "0";
                   description
                     "This leaf specifies the maximum number of other
                      syslog messages to send until resending the
                      Certificate Block.";
                 }

                 leaf sig-max-delay {
                   type uint32;
                   units "seconds";
                   default "60";
                   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 sig-number-resends {
                   type uint32;
                   default "0";
                   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 RFC 5426 is used.).";
                 }

                 leaf sig-resend-delay {
                   type uint32;

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                   units "seconds";
                   default "5";
                   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 sig-resend-count {
                   type uint32;
                   default "0";
                   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. A value of 0 means that you
                      don't resend based on the number of messages.";
                 }
               }
             }
           }
         }
       }
     }
   }
   <CODE ENDS>

                         Figure 2: Sylog YANG Model

7.  Usage Examples

7.1.  Syslog Configuration for Severity Critical

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   [note: '\' line wrapping for formatting only]

   <!--
        Enable console logging of syslogs of severity critical
   -->

   <?xml version="1.0" encoding="UTF-8"?>
   <syslog xmlns="urn:ietf:params:xml:ns:yang:ietf-syslog">
     <actions>
       <console>
         <filter>
           <facility-list>
             <facility>all</facility>
             <severity>critical</severity>
           </facility-list>
         </filter>
       </console>
     </actions>
   </syslog>

            Figure 3: Syslog Configuration for Severity Critical

7.2.  Remote Syslog Configuration

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   [note: '\' line wrapping for formatting only]

   <!--
         Enable remote logging of syslogs to udp destination
         foo.example.com for facility auth, severity error
   -->
   <?xml version="1.0" encoding="UTF-8"?>
   <syslog xmlns="urn:ietf:params:xml:ns:yang:ietf-syslog">
     <actions>
       <remote>
         <destination>
           <name>remote1</name>
           <udp>
             <udp>
               <address>foo.example.com</address>
             </udp>
           </udp>
           <filter>
             <facility-list>
               <facility>auth</facility>
               <severity>error</severity>
             </facility-list>
           </filter>
         </destination>
       </remote>
     </actions>
   </syslog>

                   Figure 4: Remote Syslog Configuration

8.  Acknowledgements

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

   Andy Bierman, Martin Bjorklund, Alex Campbell, Alex Clemm, Francis
   Dupont, Jim Gibson, Jeffrey Haas, Bob Harold, John Heasley, Giles
   Heron, Lisa Huang, Mahesh Jethanandani, Warren Kumari, Jeffrey K
   Lange, Jan Lindblad, Chris Lonvick, Alexey Melnikov, Kathleen
   Moriarty, Tom Petch, Adam Roach, Juergen Schoenwaelder, Phil Shafer,
   Yaron Sheffer, Jason Sterne, Peter Van Horne, Kent Watsen, Bert
   Wijnen, Dale R Worley, and Aleksandr Zhdankin.

9.  IANA Considerations

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9.1.  The IETF XML Registry

   This document registers one URI in the IETF XML registry [RFC3688] .
   Following the format in [RFC3688] , the following registration is
   requested:

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

9.2.  The YANG Module Names Registry

   This document registers one YANG module in the YANG Module Names
   registry [RFC8525] . Following the format in [RFC7950] , the
   following registration is requested:

      name:         ietf-syslog
      namespace:    urn:ietf:params:xml:ns:yang:ietf-syslog
      prefix:       syslog
      reference:    RFC zzzz

10.  Security Considerations

   This section is modeled after the template defined in Section 3.7.1
   of [RFC8407].

   The "ietf-syslog" YANG module specified in this document defines a
   data model that is designed to be accessed via YANG-based management
   protocols such as NETCONF [RFC6241] and RESTCONF [RFC8040].  These
   protocols have mandatory-to-implement secure transport layers (e.g.,
   Secure Shell (SSH) [RFC4252], TLS [RFC8446], and QUIC [RFC9000]) and
   mandatory-to-implement mutual authentication.

   The NETCONF access control model [RFC8341] provides the means to
   restrict access for particular NETCONF or RESTCONF users to a
   preconfigured subset of all available NETCONF or RESTCONF protocol
   operations and content.

   This module imports groupings from ietf-crypto-types YANG module
   defined in YANG Groupings for Crypto Types
   [I-D.ietf-netconf-crypto-types].  Security considerations described
   in that document apply to this module also.

   There are a number of data nodes defined in this YANG module that are
   writable/creatable/deletable (i.e., config true, which is the
   default).  These data nodes should be considered sensitive or
   vulnerable in all network environments.  Logging in particular is
   used to assess the state of systems and can be used to indicate a

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   network compromise.  If logging were to be disabled through malicious
   means, attacks may not be readily detectable.  Therefore write
   operations (e.g., edit-config) to these data nodes without proper
   protection can have a negative effect on network operations and on
   network security.

   In addition there are data nodes that require careful analysis and
   review.  These are the subtrees and data nodes and their sensitivity/
   vulnerability:

   facility-filter/pattern-match:  When writing this node,
         implementations MUST ensure that the regular expression pattern
         match is not constructed to cause a regular expression denial
         of service attack due to a pattern that causes the regular
         expression implementation to work very slowly (exponentially
         related to input size).

   remote/destination/signing/cert-signer:  When writing this subtree,
         implementations MUST NOT specify a private key that is used for
         any other purpose.

   Some of the readable data nodes in this YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control read access (e.g., via get, get-config, or
   notification) to these data nodes.  These are the subtrees and data
   nodes and their sensitivity/vulnerability:

   remote/destination/transport:  This subtree contains information
         about other hosts in the network, the services available on
         those hosts, and the TLS transport certificate properties if
         TLS is selected as the transport protocol.  Knowing that a
         service like syslog (udp/514) is enabled on the host, will
         allow a malicious user to spam the host on that port.

   remote/destination/signing:  This subtree contains information about
         the syslog message signing properties including signing
         certificate information.

   There are no RPC operations defined in this YANG module.

11.  References

11.1.  Normative References

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   [I-D.ietf-netconf-crypto-types]
              Watsen, K., "YANG Data Types and Groupings for
              Cryptography", Work in Progress, Internet-Draft, draft-
              ietf-netconf-crypto-types-34, 16 March 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              crypto-types-34>.

   [I-D.ietf-netconf-tls-client-server]
              Watsen, K., "YANG Groupings for TLS Clients and TLS
              Servers", Work in Progress, Internet-Draft, draft-ietf-
              netconf-tls-client-server-41, 16 March 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              tls-client-server-41>.

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

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

   [RFC4252]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
              January 2006, <https://www.rfc-editor.org/info/rfc4252>.

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

   [RFC5425]  Miao, F., Ed., Ma, Y., Ed., and J. Salowey, Ed.,
              "Transport Layer Security (TLS) Transport Mapping for
              Syslog", RFC 5425, DOI 10.17487/RFC5425, March 2009,
              <https://www.rfc-editor.org/info/rfc5425>.

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

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

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

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

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

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

   [RFC8089]  Kerwin, M., "The "file" URI Scheme", RFC 8089,
              DOI 10.17487/RFC8089, February 2017,
              <https://www.rfc-editor.org/info/rfc8089>.

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

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

   [RFC8343]  Bjorklund, M., "A YANG Data Model for Interface
              Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,
              <https://www.rfc-editor.org/info/rfc8343>.

   [RFC8407]  Bierman, A., "Guidelines for Authors and Reviewers of
              Documents Containing YANG Data Models", BCP 216, RFC 8407,
              DOI 10.17487/RFC8407, October 2018,
              <https://www.rfc-editor.org/info/rfc8407>.

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

   [RFC8525]  Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K.,
              and R. Wilton, "YANG Library", RFC 8525,
              DOI 10.17487/RFC8525, March 2019,
              <https://www.rfc-editor.org/info/rfc8525>.

   [RFC9000]  Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", RFC 9000,
              DOI 10.17487/RFC9000, May 2021,
              <https://www.rfc-editor.org/info/rfc9000>.

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   [Std-1003.1-2008]
              Group, I. A. T. O., ""Chapter 9: Regular Expressions". The
              Open Group Base Specifications Issue 6, IEEE Std
              1003.1-2008, 2016 Edition.", September 2016,
              <http://pubs.opengroup.org/onlinepubs/9699919799/>.

11.2.  Informative References

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

   [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore Architecture
              (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
              <https://www.rfc-editor.org/info/rfc8342>.

Appendix A.  Tree Diagrams

A.1.  Complete Tree Diagram

   [note: '\' line wrapping for formatting only]

   module: ietf-syslog
     +--rw syslog!
        +--rw actions
           +--rw console! {console-action}?
           |  +--rw filter
           |  |  +--rw facility-list* [facility severity]
           |  |     +--rw facility            union
           |  |     +--rw severity            union
           |  |     +--rw advanced-compare {select-adv-compare}?
           |  |        +--rw compare?   enumeration
           |  |        +--rw action?    identityref
           |  +--rw pattern-match?   string {select-match}?
           +--rw file {file-action}?
           |  +--rw log-file* [name]
           |     +--rw name               inet:uri
           |     +--rw filter
           |     |  +--rw facility-list* [facility severity]
           |     |     +--rw facility            union
           |     |     +--rw severity            union
           |     |     +--rw advanced-compare {select-adv-compare}?
           |     |        +--rw compare?   enumeration
           |     |        +--rw action?    identityref
           |     +--rw pattern-match?     string {select-match}?
           |     +--rw structured-data?   boolean {structured-data}?
           |     +--rw file-rotation

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           |        +--rw number-of-files?   uint32 {file-limit-size}?
           |        +--rw max-file-size?     uint32 {file-limit-size}?
           |        +--rw rollover?          uint32
           |        |       {file-limit-duration}?
           |        +--rw retention?         uint32
           |                {file-limit-duration}?
           +--rw remote {remote-action}?
              +--rw destination* [name]
                 +--rw name                 string
                 +--rw (transport)
                 |  +--:(udp)
                 |  |  +--rw udp
                 |  |     +--rw udp* [address]
                 |  |        +--rw address    inet:host
                 |  |        +--rw port?      inet:port-number
                 |  +--:(tls)
                 |     +--rw tls
                 |        +--rw tls* [address]
                 |           +--rw address                  inet:host
                 |           +--rw port?
                 |           |       inet:port-number
                 |           +--rw client-identity!
                 |           |  +--rw (auth-type)
                 |           |     +--:(certificate)
                 |           |     |        {client-ident-x509-cert}?
                 |           |     |  +--rw certificate
                 |           |     |     +--rw (inline-or-keystore)
                 |           |     |        +--:(inline)
                 |           |     |        |        {inline-definition\
   s-s
   upported}?
                 |           |     |        |  +--rw inline-definition
                 |           |     |        |     +--rw public-key-form\
   at?
                 |           |     |        |     |       identityref
                 |           |     |        |     +--rw public-key?
                 |           |     |        |     |       binary
                 |           |     |        |     +--rw private-key-for\
   mat
   ?
                 |           |     |        |     |       identityref
                 |           |     |        |     +--rw (private-key-ty\
   pe)
                 |           |     |        |     |  +--:(cleartext-pri\
   vat
   e-key)
                 |           |     |        |     |  |        {cleartex\
   t-p

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   rivate-keys}?
                 |           |     |        |     |  |  +--rw cleartext\
   -pr
   ivate-key?
                 |           |     |        |     |  |          binary
                 |           |     |        |     |  +--:(hidden-privat\
   e-k
   ey)
                 |           |     |        |     |  |        {hidden-p\
   riv
   ate-keys}?
                 |           |     |        |     |  |  +--rw hidden-pr\
   iva
   te-key?
                 |           |     |        |     |  |          empty
                 |           |     |        |     |  +--:(encrypted-pri\
   vat
   e-key)
                 |           |     |        |     |           {encrypte\
   d-p
   rivate-keys}?
                 |           |     |        |     |     +--rw encrypted\
   -pr
   ivate-key
                 |           |     |        |     |        +--rw encryp\
   ted
   -by
                 |           |     |        |     |        +--rw encryp\
   ted
   -value-format
                 |           |     |        |     |        |       iden\
   tit
   yref
                 |           |     |        |     |        +--rw encryp\
   ted
   -value
                 |           |     |        |     |                bina\
   ry
                 |           |     |        |     +--rw cert-data?
                 |           |     |        |     |       end-entity-ce\
   rt-
   cms
                 |           |     |        |     +---n certificate-exp\
   ira
   tion
                 |           |     |        |     |       {certificate-\
   exp
   iration-notification}?

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                 |           |     |        |     |  +-- expiration-dat\
   e
                 |           |     |        |     |          yang:date-\
   and
   -time
                 |           |     |        |     +---x generate-csr
                 |           |     |        |             {csr-generati\
   on}
   ?
                 |           |     |        |        +---w input
                 |           |     |        |        |  +---w csr-forma\
   t
                 |           |     |        |        |  |       identit\
   yre
   f
                 |           |     |        |        |  +---w csr-info
                 |           |     |        |        |          csr-inf\
   o
                 |           |     |        |        +--ro output
                 |           |     |        |           +--ro (csr-type\
   )
                 |           |     |        |              +--:(p10-csr\
   )
                 |           |     |        |                 +--ro p10\
   -cs
   r?
                 |           |     |        |                         p\
   10-
   csr
                 |           |     |        +--:(central-keystore)
                 |           |     |                 {central-keystore-\
   sup
   ported,asymmetric-keys}?
                 |           |     |           +--rw central-keystore-r\
   efe
   rence
                 |           |     |              +--rw asymmetric-key?\

                 |           |     |              |       ks:central-as\
   ymm
   etric-key-ref
                 |           |     |              |       {central-keys\
   tor
   e-supported,asymmetric-keys}?
                 |           |     |              +--rw certificate?
                 |           |     |                      leafref
                 |           |     +--:(raw-public-key)
                 |           |     |        {client-ident-raw-public-ke\

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   y}?
                 |           |     |  +--rw raw-private-key
                 |           |     |     +--rw (inline-or-keystore)
                 |           |     |        +--:(inline)
                 |           |     |        |        {inline-definition\
   s-s
   upported}?
                 |           |     |        |  +--rw inline-definition
                 |           |     |        |     +--rw public-key-form\
   at?
                 |           |     |        |     |       identityref
                 |           |     |        |     +--rw public-key?
                 |           |     |        |     |       binary
                 |           |     |        |     +--rw private-key-for\
   mat
   ?
                 |           |     |        |     |       identityref
                 |           |     |        |     +--rw (private-key-ty\
   pe)
                 |           |     |        |        +--:(cleartext-pri\
   vat
   e-key)
                 |           |     |        |        |        {cleartex\
   t-p
   rivate-keys}?
                 |           |     |        |        |  +--rw cleartext\
   -pr
   ivate-key?
                 |           |     |        |        |          binary
                 |           |     |        |        +--:(hidden-privat\
   e-k
   ey)
                 |           |     |        |        |        {hidden-p\
   riv
   ate-keys}?
                 |           |     |        |        |  +--rw hidden-pr\
   iva
   te-key?
                 |           |     |        |        |          empty
                 |           |     |        |        +--:(encrypted-pri\
   vat
   e-key)
                 |           |     |        |                 {encrypte\
   d-p
   rivate-keys}?
                 |           |     |        |           +--rw encrypted\
   -pr
   ivate-key

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                 |           |     |        |              +--rw encryp\
   ted
   -by
                 |           |     |        |              +--rw encryp\
   ted
   -value-format
                 |           |     |        |              |       iden\
   tit
   yref
                 |           |     |        |              +--rw encryp\
   ted
   -value
                 |           |     |        |                      bina\
   ry
                 |           |     |        +--:(central-keystore)
                 |           |     |                 {central-keystore-\
   sup
   ported,asymmetric-keys}?
                 |           |     |           +--rw central-keystore-r\
   efe
   rence?
                 |           |     |                   ks:central-asymm\
   etr
   ic-key-ref
                 |           |     +--:(tls12-psk)
                 |           |     |        {client-ident-tls12-psk}?
                 |           |     |  +--rw tls12-psk
                 |           |     |     +--rw (inline-or-keystore)
                 |           |     |     |  +--:(inline)
                 |           |     |     |  |        {inline-definition\
   s-s
   upported}?
                 |           |     |     |  |  +--rw inline-definition
                 |           |     |     |  |     +--rw key-format?
                 |           |     |     |  |     |       identityref
                 |           |     |     |  |     +--rw (key-type)
                 |           |     |     |  |        +--:(cleartext-sym\
   met
   ric-key)
                 |           |     |     |  |        |  +--rw cleartext\
   -sy
   mmetric-key?
                 |           |     |     |  |        |          binary
                 |           |     |     |  |        |          {cleart\
   ext
   -symmetric-keys}?
                 |           |     |     |  |        +--:(hidden-symmet\
   ric

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   -key)
                 |           |     |     |  |        |        {hidden-s\
   ymm
   etric-keys}?
                 |           |     |     |  |        |  +--rw hidden-sy\
   mme
   tric-key?
                 |           |     |     |  |        |          empty
                 |           |     |     |  |        +--:(encrypted-sym\
   met
   ric-key)
                 |           |     |     |  |                 {encrypte\
   d-s
   ymmetric-keys}?
                 |           |     |     |  |           +--rw encrypted\
   -sy
   mmetric-key
                 |           |     |     |  |              +--rw encryp\
   ted
   -by
                 |           |     |     |  |              +--rw encryp\
   ted
   -value-format
                 |           |     |     |  |              |       iden\
   tit
   yref
                 |           |     |     |  |              +--rw encryp\
   ted
   -value
                 |           |     |     |  |                      bina\
   ry
                 |           |     |     |  +--:(central-keystore)
                 |           |     |     |           {central-keystore-\
   sup
   ported,symmetric-keys}?
                 |           |     |     |     +--rw central-keystore-r\
   efe
   rence?
                 |           |     |     |             ks:central-symme\
   tri
   c-key-ref
                 |           |     |     +--rw id?
                 |           |     |             string
                 |           |     +--:(tls13-epsk)
                 |           |              {client-ident-tls13-epsk}?
                 |           |        +--rw tls13-epsk
                 |           |           +--rw (inline-or-keystore)
                 |           |           |  +--:(inline)

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                 |           |           |  |        {inline-definition\
   s-s
   upported}?
                 |           |           |  |  +--rw inline-definition
                 |           |           |  |     +--rw key-format?
                 |           |           |  |     |       identityref
                 |           |           |  |     +--rw (key-type)
                 |           |           |  |        +--:(cleartext-sym\
   met
   ric-key)
                 |           |           |  |        |  +--rw cleartext\
   -sy
   mmetric-key?
                 |           |           |  |        |          binary
                 |           |           |  |        |          {cleart\
   ext
   -symmetric-keys}?
                 |           |           |  |        +--:(hidden-symmet\
   ric
   -key)
                 |           |           |  |        |        {hidden-s\
   ymm
   etric-keys}?
                 |           |           |  |        |  +--rw hidden-sy\
   mme
   tric-key?
                 |           |           |  |        |          empty
                 |           |           |  |        +--:(encrypted-sym\
   met
   ric-key)
                 |           |           |  |                 {encrypte\
   d-s
   ymmetric-keys}?
                 |           |           |  |           +--rw encrypted\
   -sy
   mmetric-key
                 |           |           |  |              +--rw encryp\
   ted
   -by
                 |           |           |  |              +--rw encryp\
   ted
   -value-format
                 |           |           |  |              |       iden\
   tit
   yref
                 |           |           |  |              +--rw encryp\
   ted
   -value

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                 |           |           |  |                      bina\
   ry
                 |           |           |  +--:(central-keystore)
                 |           |           |           {central-keystore-\
   sup
   ported,symmetric-keys}?
                 |           |           |     +--rw central-keystore-r\
   efe
   rence?
                 |           |           |             ks:central-symme\
   tri
   c-key-ref
                 |           |           +--rw external-identity
                 |           |           |       string
                 |           |           +--rw hash?
                 |           |           |       tlscmn:epsk-supported-\
   has
   h
                 |           |           +--rw context?
                 |           |           |       string
                 |           |           +--rw target-protocol?
                 |           |           |       uint16
                 |           |           +--rw target-kdf?
                 |           |                   uint16
                 |           +--rw server-authentication
                 |           |  +--rw ca-certs! {server-auth-x509-cert}\
   ?
                 |           |  |  +--rw (inline-or-truststore)
                 |           |  |     +--:(inline)
                 |           |  |     |        {inline-definitions-supp\
   ort
   ed}?
                 |           |  |     |  +--rw inline-definition
                 |           |  |     |     +--rw certificate* [name]
                 |           |  |     |        +--rw name
                 |           |  |     |        |       string
                 |           |  |     |        +--rw cert-data
                 |           |  |     |        |       trust-anchor-cer\
   t-c
   ms
                 |           |  |     |        +---n certificate-expira\
   tio
   n
                 |           |  |     |                {certificate-exp\
   ira
   tion-notification}?
                 |           |  |     |           +-- expiration-date
                 |           |  |     |                   yang:date-and\

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   -ti
   me
                 |           |  |     +--:(central-truststore)
                 |           |  |              {central-truststore-supp\
   ort
   ed,certificates}?
                 |           |  |        +--rw central-truststore-refer\
   enc
   e?
                 |           |  |                ts:central-certificate\
   -ba
   g-ref
                 |           |  +--rw ee-certs! {server-auth-x509-cert}\
   ?
                 |           |  |  +--rw (inline-or-truststore)
                 |           |  |     +--:(inline)
                 |           |  |     |        {inline-definitions-supp\
   ort
   ed}?
                 |           |  |     |  +--rw inline-definition
                 |           |  |     |     +--rw certificate* [name]
                 |           |  |     |        +--rw name
                 |           |  |     |        |       string
                 |           |  |     |        +--rw cert-data
                 |           |  |     |        |       trust-anchor-cer\
   t-c
   ms
                 |           |  |     |        +---n certificate-expira\
   tio
   n
                 |           |  |     |                {certificate-exp\
   ira
   tion-notification}?
                 |           |  |     |           +-- expiration-date
                 |           |  |     |                   yang:date-and\
   -ti
   me
                 |           |  |     +--:(central-truststore)
                 |           |  |              {central-truststore-supp\
   ort
   ed,certificates}?
                 |           |  |        +--rw central-truststore-refer\
   enc
   e?
                 |           |  |                ts:central-certificate\
   -ba
   g-ref
                 |           |  +--rw raw-public-keys!

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                 |           |  |       {server-auth-raw-public-key}?
                 |           |  |  +--rw (inline-or-truststore)
                 |           |  |     +--:(inline)
                 |           |  |     |        {inline-definitions-supp\
   ort
   ed}?
                 |           |  |     |  +--rw inline-definition
                 |           |  |     |     +--rw public-key* [name]
                 |           |  |     |        +--rw name
                 |           |  |     |        |       string
                 |           |  |     |        +--rw public-key-format
                 |           |  |     |        |       identityref
                 |           |  |     |        +--rw public-key
                 |           |  |     |                binary
                 |           |  |     +--:(central-truststore)
                 |           |  |              {central-truststore-supp\
   ort
   ed,public-keys}?
                 |           |  |        +--rw central-truststore-refer\
   enc
   e?
                 |           |  |                ts:central-public-key-\
   bag
   -ref
                 |           |  +--rw tls12-psks?        empty
                 |           |  |       {server-auth-tls12-psk}?
                 |           |  +--rw tls13-epsks?       empty
                 |           |          {server-auth-tls13-epsk}?
                 |           +--rw hello-params {tlscmn:hello-params}?
                 |           |  +--rw tls-versions
                 |           |  |  +--rw min?   identityref
                 |           |  |  +--rw max?   identityref
                 |           |  +--rw cipher-suites
                 |           |     +--rw cipher-suite*
                 |           |             tlscsa:tls-cipher-suite-algo\
   rit
   hm
                 |           +--rw keepalives {tls-client-keepalives}?
                 |              +--rw peer-allowed-to-send?   empty
                 |              +--rw test-peer-aliveness!
                 |                 +--rw max-wait?       uint16
                 |                 +--rw max-attempts?   uint8
                 +--rw filter
                 |  +--rw facility-list* [facility severity]
                 |     +--rw facility            union
                 |     +--rw severity            union
                 |     +--rw advanced-compare {select-adv-compare}?
                 |        +--rw compare?   enumeration

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                 |        +--rw action?    identityref
                 +--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! {signed-messages}?
                    +--rw cert-signers
                       +--rw cert-signer* [name]
                       |  +--rw name              string
                       |  +--rw cert
                       |  |  +--rw public-key-format?
                       |  |  |       identityref
                       |  |  +--rw public-key?                    binar\
   y
                       |  |  +--rw private-key-format?
                       |  |  |       identityref
                       |  |  +--rw (private-key-type)
                       |  |  |  +--:(cleartext-private-key)
                       |  |  |  |        {cleartext-private-keys}?
                       |  |  |  |  +--rw cleartext-private-key?   binar\
   y
                       |  |  |  +--:(hidden-private-key)
                       |  |  |  |        {hidden-private-keys}?
                       |  |  |  |  +--rw hidden-private-key?      empty\

                       |  |  |  +--:(encrypted-private-key)
                       |  |  |           {encrypted-private-keys}?
                       |  |  |     +--rw encrypted-private-key
                       |  |  |        +--rw encrypted-by
                       |  |  |        +--rw encrypted-value-format
                       |  |  |        |       identityref
                       |  |  |        +--rw encrypted-value
                       |  |  |                binary
                       |  |  +--rw cert-data?
                       |  |  |       end-entity-cert-cms
                       |  |  +---n certificate-expiration
                       |  |  |       {certificate-expiration-notificati\
   on}
   ?
                       |  |  |  +-- expiration-date
                       |  |  |          yang:date-and-time
                       |  |  +---x generate-csr {csr-generation}?
                       |  |     +---w input
                       |  |     |  +---w csr-format    identityref
                       |  |     |  +---w csr-info      csr-info
                       |  |     +--ro output
                       |  |        +--ro (csr-type)

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                       |  |           +--:(p10-csr)
                       |  |              +--ro p10-csr?   p10-csr
                       |  +--rw hash-algorithm?   enumeration
                       +--rw cert-initial-repeat?   uint32
                       +--rw cert-resend-delay?     uint32
                       +--rw cert-resend-count?     uint32
                       +--rw sig-max-delay?         uint32
                       +--rw sig-number-resends?    uint32
                       +--rw sig-resend-delay?      uint32
                       +--rw sig-resend-count?      uint32

Appendix B.  Implementer Guidelines

B.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):

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   [note: '\' line wrapping for formatting only]

   module example-vendor-syslog-types {
     namespace "http://example.com/ns/vendor-syslog-types";
     prefix vendor-syslogtypes;

     import ietf-syslog {
       prefix syslog;
     }

     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 2024-03-19 {
       description
         "Version 1.0";
       reference
         "Vendor SYSLOG Types: SYSLOG YANG Model";
     }

     identity vendor_specific_type_1 {
       base syslog:syslog-facility;
       description
         "Adding vendor specific type 1 to syslog-facility";
     }

     identity vendor_specific_type_2 {
       base syslog:syslog-facility;
       description
         "Adding vendor specific type 2 to syslog-facility";
     }
   }

B.2.  Syslog Terminal Output

   Terminal output with requirements more complex than the console
   subtree currently provides, are expected to be supported via vendor
   extensions rather than handled via the file subtree.

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B.3.  Syslog File Naming Convention

   The syslog/file/log-file/file-rotation container contains
   configuration parameters for syslog file rotation.  This section
   describes how these fields might be used by an implementer to name
   syslog files in a rotation process.  This information is offered as
   an informative guide only.

   When an active syslog file with a name specified by log-file/name,
   reaches log-file/max-file-size and/or syslog events arrive after the
   period specified by log-file/rollover, the logging system can close
   the file, can compress it, and can name the archive file <log-file/
   name>.0.gz.  The logging system can then open a new active syslog
   file <log-file/name>.

   When the new syslog file reaches either of the size limits referenced
   above, <log-file/name>.0.gz can be renamed <log-file/name>.1.gz and
   the new syslog file can be closed, compressed and renamed <log-file/
   name>.0.gz.  Each time that a new syslog file is closed, each of the
   prior syslog archive files named <log-file/name>.<n>.gz can be
   renamed to <log-file/name>.<n + 1>.gz.

   Removal of archive log files could occur when either or both:

   - log-file/number-of-files specified - the logging system can create
   up to log-file/number-of-files syslog archive files after which, the
   contents of the oldest archived file could be overwritten.

   - log-file/retention specified - the logging system can remove those
   syslog archive files whose file expiration time (file creation time
   plus the specified log-file/retention time) is prior to the current
   time.

Authors' Addresses

   Joe Clarke (editor)
   Cisco
   United States of America
   Email: jclarke@cisco.com

   Mahesh Jethanandani (editor)
   Kloud Services
   United States of America
   Email: mjethanandani@gmail.com

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   Clyde Wildes (editor)
   Cisco Systems Inc.
   170 West Tasman Drive
   San Jose, CA 95134
   United States of America
   Phone: +1 415 819-6111
   Email: clyde@clydewildes.com

   Kiran Koushik (editor)
   Verizon Wireless
   500 W Dove Rd.
   Southlake, TX 76092
   United States of America
   Phone: +1 512 650-0210
   Email: kirankoushik.agraharasreenivasa@verizonwireless.com

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