Cisco Systems Inc.

170 West Tasman Drive San Jose CA 95134 US +1 408 527-2672 cwildes@cisco.com

Verizon Wireless

500 W Dove Rd. Southlake TX 76092 US +1 512 650-0210 kirankoushik.agraharasreenivasa@verizonwireless.com

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

Introduction This document defines a YANG 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 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. 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 , and are used in this RFC. The YANG model in this document conforms to the Network Management Datastore Architecture defined in [draft-ietf-netmod-revised-datastores].

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 when, and only when, they appear in all capitals, as shown here.

Terminology The term "originator" is defined in : an "originator" generates syslog content to be carried in a message. The term "relay" is defined in : a "relay" forwards messages, accepting messages from originators or other relays and sending them to collectors or other relays The term "collectors" is defined in : a "collector" gathers syslog content for further analysis. The term "action" refers to the processing that takes place for each syslog message received.

NDMA Compliance The YANG model in this document conforms to the Network Management Datastore Architecture defined in I-D.ietf-netmod-revised-datastores.

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-keystore --> the assigned RFC value for draft-ietf-netconf-keystore
• 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
• I-D.ietf-netmod-revised-datastores --> the assigned RFC value for draft-ietf-netmod-revised-datastores

Design of the Syslog Model The syslog model was designed by comparing various syslog features implemented by various vendors' in different implementations. This document addresses the common leafs between implementations and creates a common model, which can be augmented with proprietary features, if necessary. This model is designed to be very simple for maximum flexibility. Some optional features are defined in this document to specify functionality that is present in specific vendor configurations. Syslog consists of originators and collectors. The following diagram shows syslog messages flowing from originators, to collectors where filtering can take place.

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 field. A syslog message is processed if:

• 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 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 or block 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 A.1).

Syslog Module A simplified graphical representation of the data model is used in this document. Please see [I-D.ietf-netmod-yang-tree-diagrams] for tree diagram notation.

ietf-syslog Module Tree

Syslog YANG Module

The ietf-syslog Module This module imports typedefs from , , groupings from , and , and it references , , , , , , and . WG List: Editor: Kiran Agrahara Sreenivasa Editor: Clyde Wildes "; description "This module contains a collection of YANG definitions for syslog configuration. Copyright (c) 2018 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 zzzz (http://tools.ietf.org/html/rfczzzz); see the RFC itself for full legal notices."; revision 2018-03-15 { 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."; } 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 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"; } 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 "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)."; 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)."; 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)."; reference "RFC 5424: The Syslog Protocol"; } 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; 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."; } leaf action { type enumeration { enum log { description "This enum specifies that if the compare operation is true the message will be logged."; } enum block { description "This enum specifies that if the compare operation is true the message will not be logged."; } } default log; description "The action can be used to specify if the message should be logged or blocked based on the outcome of the compare operation."; } 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 [ ...] 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 facility-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 { 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 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:.*'; } 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."; } 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"; 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 "; 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 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 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 ks:private-key-grouping; uses ks:certificate-grouping; description "This is the certificate that is periodically sent to the remote receiver. Selection of the certificate also implicitly selects the private key used to sign the syslog messages."; } 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; 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; 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."; } } } } } } } } ]]> Figure 3. ietf-syslog Module

Usage Examples

ietf-syslog Examples Requirement: Enable console logging of syslogs of severity critical all critical ]]> Enable remote logging of syslogs to udp destination foo.example.com for facility auth, severity error remote1

foo.example.com

auth error ]]>

IANA Considerations

The IETF XML Registry This document registers one URI in the IETF XML registry . Following the format in , the following registration is requested:

The YANG Module Names Registry This document registers one YANG module in the YANG Module Names registry . Following the format in , the following registration is requested:

Security Considerations The YANG module defined in this document is designed to be accessed via YANG based management protocols, such as NETCONF and RESTCONF . Both of these protocols have mandatory-to-implement secure transport layers (e.g., SSH, TLS) with mutual authentication. The NETCONF access control model (NACM) provides the means to restrict access for particular users to a pre-configured subset of all available protocol operations and content. 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 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, and the TLS transport certificate properties if TLS is selected as the transport protocol.

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.

References Normative References This document defines a YANG 1.1 module called "ietf-keystore" that enables centralized configuration of asymmetric keys and their associated certificates, and notification for when configured certificates are about to expire. This document defines three YANG modules: the first defines groupings for a generic TLS client, the second defines groupings for a generic TLS server, and the third defines common identities and groupings used by both the client and the server. It is intended that these groupings will be used by applications using the TLS protocol. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document describes the syslog protocol, which is used to convey event notification messages. This protocol utilizes a layered architecture, which allows the use of any number of transport protocols for transmission of syslog messages. It also provides a message format that allows vendor-specific extensions to be provided in a structured way. This document has been written with the original design goals for traditional syslog in mind. The need for a new layered specification has arisen because standardization efforts for reliable and secure syslog extensions suffer from the lack of a Standards-Track and transport-independent RFC. Without this document, each other standard needs to define its own syslog packet format and transport mechanism, which over time will introduce subtle compatibility issues. This document tries to provide a foundation that syslog extensions can build on. This layered architecture approach also provides a solid basis that allows code to be written once for each syslog feature rather than once for each transport. [STANDARDS-TRACK] This document describes the use of Transport Layer Security (TLS) to provide a secure connection for the transport of syslog messages. This document describes the security threats to syslog and how TLS can be used to counter such threats. [STANDARDS-TRACK] This document describes the transport for syslog messages over UDP/ IPv4 or UDP/IPv6. The syslog protocol layered architecture provides for support of any number of transport mappings. However, for interoperability purposes, syslog protocol implementers are required to support this transport mapping. [STANDARDS-TRACK] This document describes a mechanism to add origin authentication, message integrity, replay resistance, message sequencing, and detection of missing messages to the transmitted syslog messages. This specification is intended to be used in conjunction with the work defined in RFC 5424, "The Syslog Protocol". [STANDARDS-TRACK] This document introduces a collection of common data types to be used with the YANG data modeling language. This document obsoletes RFC 6021. This document defines a YANG data model for the management of network interfaces. It is expected that interface-type-specific data models augment the generic interfaces data model defined in this document. The data model includes definitions for configuration and system state (status information and counters for the collection of statistics). The YANG model in this document conforms to the Network Management Datastore Architecture defined in I-D.ietf-netmod-revised-datastores. This document obsoletes RFC 7223. This document describes a YANG library that provides information about all the YANG modules used by a network management server (e.g., a Network Configuration Protocol (NETCONF) server). Simple caching mechanisms are provided to allow clients to minimize retrieval of this information. YANG is a data modeling language used to model configuration data, state data, Remote Procedure Calls, and notifications for network management protocols. This document describes the syntax and semantics of version 1.1 of the YANG language. YANG version 1.1 is a maintenance release of the YANG language, addressing ambiguities and defects in the original specification. There are a small number of backward incompatibilities from YANG version 1. This document also specifies the YANG mappings to the Network Configuration Protocol (NETCONF). This document provides a more complete specification of the "file" Uniform Resource Identifier (URI) scheme and replaces the very brief definition in Section 3.10 of RFC 1738. It defines a common syntax that is intended to interoperate across the broad spectrum of existing usages. At the same time, it notes some other current practices around the use of file URIs. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. The Open Group Informative References This document captures the current syntax used in YANG module Tree Diagrams. The purpose of this document is to provide a single location for this definition. This syntax may be updated from time to time based on the evolution of the YANG language. Datastores are a fundamental concept binding the data models written in the YANG data modeling language to network management protocols such as NETCONF and RESTCONF. This document defines an architectural framework for datastores based on the experience gained with the initial simpler model, addressing requirements that were not well supported in the initial model. This document updates RFC 7950. This document describes an IANA maintained registry for IETF standards which use Extensible Markup Language (XML) related items such as Namespaces, Document Type Declarations (DTDs), Schemas, and Resource Description Framework (RDF) Schemas. The Network Configuration Protocol (NETCONF) defined in this document provides mechanisms to install, manipulate, and delete the configuration of network devices. It uses an Extensible Markup Language (XML)-based data encoding for the configuration data as well as the protocol messages. The NETCONF protocol operations are realized as remote procedure calls (RPCs). This document obsoletes RFC 4741. [STANDARDS-TRACK] The standardization of network configuration interfaces for use with the Network Configuration Protocol (NETCONF) requires a structured and secure operating environment that promotes human usability and multi-vendor interoperability. There is a need for standard mechanisms to restrict NETCONF protocol access for particular users to a pre-configured subset of all available NETCONF protocol operations and content. This document defines such an access control model. [STANDARDS-TRACK] This document describes an HTTP-based protocol that provides a programmatic interface for accessing data defined in YANG, using the datastore concepts defined in the Network Configuration Protocol (NETCONF).

Implementer Guidelines

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):

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.

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.

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.