A YANG Data Model for System Management

This document defines a YANG data model for the configuration and identification of some common properties within a device containing a Network Configuration Protocol (NETCONF) server. Devices that are managed by NETCONF and perhaps other mechanisms have common properties that need to be configured and monitored in a standard way. The "ietf&nbhy;system" YANG module defined in this document provides the following features: configuration and monitoring of system identification configuration and monitoring of system time-of-day configuration of user authentication configuration of local users configuration of the DNS resolver system control operations (shutdown, restart, setting time)

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, . The following terms are defined in and are not redefined here: client configuration data server state data The following terms are defined in and are not redefined here: augment data model

A simplified graphical representation of the data model is used in this document. The meaning of the symbols in these diagrams is as follows: Brackets "[" and "]" enclose list keys. Abbreviations before data node names: "rw" means configuration (read-write), and "ro" means state data (read-only). Symbols after data node names: "?" means an optional node, "!" means a presence container, and "*" denotes a list and leaf-list. Parentheses enclose choice and case nodes, and case nodes are also marked with a colon (":"). Ellipsis ("...") stands for contents of subtrees that are not shown.

There are many common properties used to identify devices, operating systems, software versions, etc. that need to be supported in the system data module. These objects are defined as operational state data, and the information returned by the server is intended to be specific to the device vendor. Some user-configurable administrative strings are also provided, such as the system location and description.

Management of the date and time used by the system needs to be supported. The use of one or more NTP servers to automatically set the system date and time needs to be possible. Utilization of the Time Zone Database also needs to be supported. It should be possible to configure the system to use NTP.

The authentication mechanism needs to support password authentication over RADIUS in order to support deployment scenarios with centralized authentication servers. Additionally, for scenarios when no centralized authentication server exists or for situations where the centralized authentication server cannot be reached from the device, local users need to be supported. Since the mandatory transport protocol for NETCONF is Secure Shell (SSH) , the authentication model needs to support SSH's "publickey" and "password" authentication methods . The model for authentication configuration should be flexible enough to support authentication methods defined by other standards documents or by vendors. It should be possible to configure the system authentication properties.

The configuration of the DNS resolver within the system containing the NETCONF server is required in order to control how domain names are resolved.

A few operations are needed to support common tasks such as restarting the device or setting the system date and time.

The data model for system identification has the following structure:

The data model for system time management has the following structure:

New "case" statements can be added in future revisions of this data model, or through augmentation by some other data model.

The data model for configuration of the DNS resolver has the following structure:

New "case" statements can be added in future revisions of this data model, or through augmentation by some other data model.

The data model for configuration of the RADIUS client has the following structure:

New "case" statements can be added in future revisions of this data model, or through augmentation by some other data model.

This document defines three authentication methods for use with NETCONF: publickey for local users over SSH password for local users over any secure transport password for RADIUS users over any secure transport Additional methods can be defined by other standards documents or by vendors. This document defines two optional YANG features: "local&nbhy;users" and "radius&nbhy;authentication", which the server advertises to indicate support for configuring local users on the device and support for using RADIUS for authentication, respectively. The authentication parameters defined in this document are primarily used to configure authentication of NETCONF users but MAY also be used by other interfaces, e.g., a command line interface or a web-based user interface. The data model for user authentication has the following structure:

If the NETCONF server advertises the "local&nbhy;users" feature, configuration of local users and their SSH public keys is supported in the /system/authentication/user list. Public key authentication is requested by the SSH client. If the "local&nbhy;users" feature is supported, then when a NETCONF client starts an SSH session towards the server using the "publickey" authentication "method name" , the SSH server looks up the user name given in the SSH authentication request in the /system/authentication/user list and verifies the key as described in .

If the NETCONF server advertises the "local&nbhy;users" feature, configuration of local users and their passwords is supported in the /system/authentication/user list. For NETCONF transport protocols that support password authentication, the leaf-list "user&nbhy;authentication&nbhy;order" is used to control whether or not local user password authentication should be used. In SSH, password authentication is requested by the client. Other NETCONF transport protocols MAY also support password authentication. When local user password authentication is requested, the NETCONF transport looks up the user name provided by the client in the /system/authentication/user list and verifies the password.

If the NETCONF server advertises the "radius&nbhy;authentication" feature, the device supports user authentication using RADIUS. For NETCONF transport protocols that support password authentication, the leaf-list "user&nbhy;authentication&nbhy;order" is used to control whether or not RADIUS password authentication should be used. In SSH, password authentication is requested by the client. Other NETCONF transport protocols MAY also support password authentication.

The following operations are defined:

Two protocol operations are included to restart or shut down the system. The 'system&nbhy;restart' operation can be used to restart the entire system (not just the NETCONF server). The 'system&nbhy;shutdown' operation can be used to power off the entire system.

If a device implements the SNMPv2-MIB , there are two objects that MAY be mapped by the implementation. See the YANG module definition in for details. The following table lists the YANG data nodes with corresponding objects in the SNMPv2-MIB. YANG data node SNMPv2-MIB object contact sysContact location sysLocation

This YANG module references , , and . <CODE BEGINS> file "iana-crypt-hash@2014-04-04.yang"

"; description "This YANG module defines a type for storing passwords using a hash function and features to indicate which hash functions are supported by an implementation. The latest revision of this YANG module can be obtained from the IANA web site. Requests for new values should be made to IANA via email (iana@iana.org). Copyright (c) 2014 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Simplified BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info). The initial version of this YANG module is part of RFC 7317; see the RFC itself for full legal notices."; revision 2014-04-04 { description "Initial revision."; reference "RFC 7317: A YANG Data Model for System Management"; } typedef crypt-hash { type string { pattern '$0$.*' + '|$1$[a-zA-Z0-9./]{1,8}$[a-zA-Z0-9./]{22}' + '|$5$(rounds=\d+$)?[a-zA-Z0-9./]{1,16}$[a-zA-Z0-9./]{43}' + '|$6$(rounds=\d+$)?[a-zA-Z0-9./]{1,16}$[a-zA-Z0-9./]{86}'; } description "The crypt-hash type is used to store passwords using a hash function. The algorithms for applying the hash function and encoding the result are implemented in various UNIX systems as the function crypt(3). A value of this type matches one of the forms: $0$ $$$ $$$$ The '$0$' prefix signals that the value is clear text. When such a value is received by the server, a hash value is calculated, and the string '$$$' or $$$$ is prepended to the result. This value is stored in the configuration data store. If a value starting with '$$', where is not '0', is received, the server knows that the value already represents a hashed value and stores it 'as is' in the data store. When a server needs to verify a password given by a user, it finds the stored password hash string for that user, extracts the salt, and calculates the hash with the salt and given password as input. If the calculated hash value is the same as the stored value, the password given by the client is accepted. This type defines the following hash functions: id | hash function | feature ---+---------------+------------------- 1 | MD5 | crypt-hash-md5 5 | SHA-256 | crypt-hash-sha-256 6 | SHA-512 | crypt-hash-sha-512 The server indicates support for the different hash functions by advertising the corresponding feature."; reference "IEEE Std 1003.1-2008 - crypt() function RFC 1321: The MD5 Message-Digest Algorithm FIPS.180-4.2012: Secure Hash Standard (SHS)"; } feature crypt-hash-md5 { description "Indicates that the device supports the MD5 hash function in 'crypt-hash' values."; reference "RFC 1321: The MD5 Message-Digest Algorithm"; } feature crypt-hash-sha-256 { description "Indicates that the device supports the SHA-256 hash function in 'crypt-hash' values."; reference "FIPS.180-4.2012: Secure Hash Standard (SHS)"; } feature crypt-hash-sha-512 { description "Indicates that the device supports the SHA-512 hash function in 'crypt-hash' values."; reference "FIPS.180-4.2012: Secure Hash Standard (SHS)"; } } ]]> <CODE ENDS>

This YANG module imports YANG extensions from and imports YANG types from . It also references , , , , , and . <CODE BEGINS> file "ietf-system@2014-05-14.yang"

WG List: WG Chair: Thomas Nadeau WG Chair: Juergen Schoenwaelder Editor: Andy Bierman Editor: Martin Bjorklund "; description "This module contains a collection of YANG definitions for the configuration and identification of some common system properties within a device containing a NETCONF server. This includes data node definitions for system identification, time-of-day management, user management, DNS resolver configuration, and some protocol operations for system management. Copyright (c) 2014 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Simplified BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info). This version of this YANG module is part of RFC 7317; see the RFC itself for full legal notices."; revision 2014-05-14 { description "Initial revision."; reference "RFC 7317: A YANG Data Model for System Management"; } /* * Typedefs */ typedef timezone-name { type string; description "A time zone name as used by the Time Zone Database, sometimes referred to as the 'Olson Database'. The exact set of valid values is an implementation-specific matter. Client discovery of the exact set of time zone names for a particular server is out of scope."; reference "RFC 6557: Procedures for Maintaining the Time Zone Database"; } /* * Features */ feature radius { description "Indicates that the device can be configured as a RADIUS client."; reference "RFC 2865: Remote Authentication Dial In User Service (RADIUS)"; } feature authentication { description "Indicates that the device supports configuration of user authentication."; } feature local-users { if-feature authentication; description "Indicates that the device supports configuration of local user authentication."; } feature radius-authentication { if-feature radius; if-feature authentication; description "Indicates that the device supports configuration of user authentication over RADIUS."; reference "RFC 2865: Remote Authentication Dial In User Service (RADIUS) RFC 5607: Remote Authentication Dial-In User Service (RADIUS) Authorization for Network Access Server (NAS) Management"; } feature ntp { description "Indicates that the device can be configured to use one or more NTP servers to set the system date and time."; } feature ntp-udp-port { if-feature ntp; description "Indicates that the device supports the configuration of the UDP port for NTP servers. This is a 'feature', since many implementations do not support any port other than the default port."; } feature timezone-name { description "Indicates that the local time zone on the device can be configured to use the TZ database to set the time zone and manage daylight saving time."; reference "RFC 6557: Procedures for Maintaining the Time Zone Database"; } feature dns-udp-tcp-port { description "Indicates that the device supports the configuration of the UDP and TCP port for DNS servers. This is a 'feature', since many implementations do not support any port other than the default port."; } /* * Identities */ identity authentication-method { description "Base identity for user authentication methods."; } identity radius { base authentication-method; description "Indicates user authentication using RADIUS."; reference "RFC 2865: Remote Authentication Dial In User Service (RADIUS) RFC 5607: Remote Authentication Dial-In User Service (RADIUS) Authorization for Network Access Server (NAS) Management"; } identity local-users { base authentication-method; description "Indicates password-based authentication of locally configured users."; } identity radius-authentication-type { description "Base identity for RADIUS authentication types."; } identity radius-pap { base radius-authentication-type; description "The device requests Password Authentication Protocol (PAP) authentication from the RADIUS server."; reference "RFC 2865: Remote Authentication Dial In User Service (RADIUS)"; } identity radius-chap { base radius-authentication-type; description "The device requests Challenge Handshake Authentication Protocol (CHAP) authentication from the RADIUS server."; reference "RFC 2865: Remote Authentication Dial In User Service (RADIUS)"; } /* * Configuration data nodes */ container system { description "System group configuration."; leaf contact { type string; description "The administrator contact information for the system. A server implementation MAY map this leaf to the sysContact MIB object. Such an implementation needs to use some mechanism to handle the differences in size and characters allowed between this leaf and sysContact. The definition of such a mechanism is outside the scope of this document."; reference "RFC 3418: Management Information Base (MIB) for the Simple Network Management Protocol (SNMP) SNMPv2-MIB.sysContact"; } leaf hostname { type inet:domain-name; description "The name of the host. This name can be a single domain label or the fully qualified domain name of the host."; } leaf location { type string; description "The system location. A server implementation MAY map this leaf to the sysLocation MIB object. Such an implementation needs to use some mechanism to handle the differences in size and characters allowed between this leaf and sysLocation. The definition of such a mechanism is outside the scope of this document."; reference "RFC 3418: Management Information Base (MIB) for the Simple Network Management Protocol (SNMP) SNMPv2-MIB.sysLocation"; } container clock { description "Configuration of the system date and time properties."; choice timezone { description "The system time zone information."; case timezone-name { if-feature timezone-name; leaf timezone-name { type timezone-name; description "The TZ database name to use for the system, such as 'Europe/Stockholm'."; } } case timezone-utc-offset { leaf timezone-utc-offset { type int16 { range "-1500 .. 1500"; } units "minutes"; description "The number of minutes to add to UTC time to identify the time zone for this system. For example, 'UTC - 8:00 hours' would be represented as '-480'. Note that automatic daylight saving time adjustment is not provided if this object is used."; } } } } container ntp { if-feature ntp; presence "Enables the NTP client unless the 'enabled' leaf (which defaults to 'true') is set to 'false'"; description "Configuration of the NTP client."; leaf enabled { type boolean; default true; description "Indicates that the system should attempt to synchronize the system clock with an NTP server from the 'ntp/server' list."; } list server { key name; description "List of NTP servers to use for system clock synchronization. If '/system/ntp/enabled' is 'true', then the system will attempt to contact and utilize the specified NTP servers."; leaf name { type string; description "An arbitrary name for the NTP server."; } choice transport { mandatory true; description "The transport-protocol-specific parameters for this server."; case udp { container udp { description "Contains UDP-specific configuration parameters for NTP."; leaf address { type inet:host; mandatory true; description "The address of the NTP server."; } leaf port { if-feature ntp-udp-port; type inet:port-number; default 123; description "The port number of the NTP server."; } } } } leaf association-type { type enumeration { enum server { description "Use client association mode. This device will not provide synchronization to the configured NTP server."; } enum peer { description "Use symmetric active association mode. This device may provide synchronization to the configured NTP server."; } enum pool { description "Use client association mode with one or more of the NTP servers found by DNS resolution of the domain name given by the 'address' leaf. This device will not provide synchronization to the servers."; } } default server; description "The desired association type for this NTP server."; } leaf iburst { type boolean; default false; description "Indicates whether this server should enable burst synchronization or not."; } leaf prefer { type boolean; default false; description "Indicates whether this server should be preferred or not."; } } } container dns-resolver { description "Configuration of the DNS resolver."; leaf-list search { type inet:domain-name; ordered-by user; description "An ordered list of domains to search when resolving a host name."; } list server { key name; ordered-by user; description "List of the DNS servers that the resolver should query. When the resolver is invoked by a calling application, it sends the query to the first name server in this list. If no response has been received within 'timeout' seconds, the resolver continues with the next server in the list. If no response is received from any server, the resolver continues with the first server again. When the resolver has traversed the list 'attempts' times without receiving any response, it gives up and returns an error to the calling application. Implementations MAY limit the number of entries in this list."; leaf name { type string; description "An arbitrary name for the DNS server."; } choice transport { mandatory true; description "The transport-protocol-specific parameters for this server."; case udp-and-tcp { container udp-and-tcp { description "Contains UDP- and TCP-specific configuration parameters for DNS."; reference "RFC 1035: Domain Names - Implementation and Specification RFC 5966: DNS Transport over TCP - Implementation Requirements"; leaf address { type inet:ip-address; mandatory true; description "The address of the DNS server."; } leaf port { if-feature dns-udp-tcp-port; type inet:port-number; default 53; description "The UDP and TCP port number of the DNS server."; } } } } } container options { description "Resolver options. The set of available options has been limited to those that are generally available across different resolver implementations and generally useful."; leaf timeout { type uint8 { range "1..max"; } units "seconds"; default "5"; description "The amount of time the resolver will wait for a response from each remote name server before retrying the query via a different name server."; } leaf attempts { type uint8 { range "1..max"; } default "2"; description "The number of times the resolver will send a query to all of its name servers before giving up and returning an error to the calling application."; } } } container radius { if-feature radius; description "Configuration of the RADIUS client."; list server { key name; ordered-by user; description "List of RADIUS servers used by the device. When the RADIUS client is invoked by a calling application, it sends the query to the first server in this list. If no response has been received within 'timeout' seconds, the client continues with the next server in the list. If no response is received from any server, the client continues with the first server again. When the client has traversed the list 'attempts' times without receiving any response, it gives up and returns an error to the calling application."; leaf name { type string; description "An arbitrary name for the RADIUS server."; } choice transport { mandatory true; description "The transport-protocol-specific parameters for this server."; case udp { container udp { description "Contains UDP-specific configuration parameters for RADIUS."; leaf address { type inet:host; mandatory true; description "The address of the RADIUS server."; } leaf authentication-port { type inet:port-number; default "1812"; description "The port number of the RADIUS server."; } leaf shared-secret { type string; mandatory true; nacm:default-deny-all; description "The shared secret, which is known to both the RADIUS client and server."; reference "RFC 2865: Remote Authentication Dial In User Service (RADIUS)"; } } } } leaf authentication-type { type identityref { base radius-authentication-type; } default radius-pap; description "The authentication type requested from the RADIUS server."; } } container options { description "RADIUS client options."; leaf timeout { type uint8 { range "1..max"; } units "seconds"; default "5"; description "The number of seconds the device will wait for a response from each RADIUS server before trying with a different server."; } leaf attempts { type uint8 { range "1..max"; } default "2"; description "The number of times the device will send a query to all of its RADIUS servers before giving up."; } } } container authentication { nacm:default-deny-write; if-feature authentication; description "The authentication configuration subtree."; leaf-list user-authentication-order { type identityref { base authentication-method; } must '(. != "sys:radius" or ../../radius/server)' { error-message "When 'radius' is used, a RADIUS server" + " must be configured."; description "When 'radius' is used as an authentication method, a RADIUS server must be configured."; } ordered-by user; description "When the device authenticates a user with a password, it tries the authentication methods in this leaf-list in order. If authentication with one method fails, the next method is used. If no method succeeds, the user is denied access. An empty user-authentication-order leaf-list still allows authentication of users using mechanisms that do not involve a password. If the 'radius-authentication' feature is advertised by the NETCONF server, the 'radius' identity can be added to this list. If the 'local-users' feature is advertised by the NETCONF server, the 'local-users' identity can be added to this list."; } list user { if-feature local-users; key name; description "The list of local users configured on this device."; leaf name { type string; description "The user name string identifying this entry."; } leaf password { type ianach:crypt-hash; description "The password for this entry."; } list authorized-key { key name; description "A list of public SSH keys for this user. These keys are allowed for SSH authentication, as described in RFC 4253."; reference "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol"; leaf name { type string; description "An arbitrary name for the SSH key."; } leaf algorithm { type string; mandatory true; description "The public key algorithm name for this SSH key. Valid values are the values in the IANA 'Secure Shell (SSH) Protocol Parameters' registry, Public Key Algorithm Names."; reference "IANA 'Secure Shell (SSH) Protocol Parameters' registry, Public Key Algorithm Names"; } leaf key-data { type binary; mandatory true; description "The binary public key data for this SSH key, as specified by RFC 4253, Section 6.6, i.e.: string certificate or public key format identifier byte[n] key/certificate data."; reference "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol"; } } } } } /* * Operational state data nodes */ container system-state { config false; description "System group operational state."; container platform { description "Contains vendor-specific information for identifying the system platform and operating system."; reference "IEEE Std 1003.1-2008 - sys/utsname.h"; leaf os-name { type string; description "The name of the operating system in use - for example, 'Linux'."; reference "IEEE Std 1003.1-2008 - utsname.sysname"; } leaf os-release { type string; description "The current release level of the operating system in use. This string MAY indicate the OS source code revision."; reference "IEEE Std 1003.1-2008 - utsname.release"; } leaf os-version { type string; description "The current version level of the operating system in use. This string MAY indicate the specific OS build date and target variant information."; reference "IEEE Std 1003.1-2008 - utsname.version"; } leaf machine { type string; description "A vendor-specific identifier string representing the hardware in use."; reference "IEEE Std 1003.1-2008 - utsname.machine"; } } container clock { description "Monitoring of the system date and time properties."; leaf current-datetime { type yang:date-and-time; description "The current system date and time."; } leaf boot-datetime { type yang:date-and-time; description "The system date and time when the system last restarted."; } } } rpc set-current-datetime { nacm:default-deny-all; description "Set the /system-state/clock/current-datetime leaf to the specified value. If the system is using NTP (i.e., /system/ntp/enabled is set to 'true'), then this operation will fail with error-tag 'operation-failed' and error-app-tag value of 'ntp-active'."; input { leaf current-datetime { type yang:date-and-time; mandatory true; description "The current system date and time."; } } } rpc system-restart { nacm:default-deny-all; description "Request that the entire system be restarted immediately. A server SHOULD send an rpc reply to the client before restarting the system."; } rpc system-shutdown { nacm:default-deny-all; description "Request that the entire system be shut down immediately. A server SHOULD send an rpc reply to the client before shutting down the system."; } } ]]> <CODE ENDS>

IANA has created an IANA-maintained YANG module called "iana&nbhy;crypt&nbhy;hash", based on the contents of , which will allow for new hash algorithms to be added to the type "crypt&nbhy;hash". The registration procedure will be Expert Review, as defined by . This document registers two URIs in the "IETF XML Registry" . Following the format in RFC 3688, the following registrations have been made.

This document registers two YANG modules in the "YANG Module Names" registry .

The YANG modules defined in this memo are designed to be accessed via the NETCONF protocol . The lowest NETCONF layer is the secure transport layer and the mandatory to implement secure transport is SSH . The NETCONF access control model provides the means to restrict access for particular NETCONF users to a pre-configured subset of all available NETCONF protocol operations and content. There are a number of data nodes defined in the "ietf&nbhy;system" YANG module which are writable/creatable/deletable (i.e., config true, which is the default). These data nodes may be considered sensitive or vulnerable in some network environments. Write operations (e.g., edit-config) to these data nodes without proper protection can have a negative effect on network operations. These are the subtrees and data nodes and their sensitivity/vulnerability: /system/clock/timezone: This choice contains the objects used to control the time zone used by the device. /system/ntp: This container contains the objects used to control the Network Time Protocol servers used by the device. /system/dns-resolver: This container contains the objects used to control the Domain Name System servers used by the device. /system/radius: This container contains the objects used to control the Remote Authentication Dial-In User Service servers used by the device. /system/authentication/user-authentication-order: This leaf controls how user login attempts are authenticated by the device. /system/authentication/user: This list contains the local users enabled on the system. Some of the readable data nodes in the "ietf&nbhy;system" 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&nbhy;config or notification) to these data nodes. These are the subtrees and data nodes and their sensitivity/vulnerability: /system/platform: This container has objects that may help identify the specific NETCONF server and/or operating system implementation used on the device. /system/authentication/user: This list has objects that may help identify the specific user names and password information in use on the device. Some of the RPC operations in the "ietf&nbhy;system" YANG module may be considered sensitive or vulnerable in some network environments. It is thus important to control access to these operations. These are the operations and their sensitivity/vulnerability: set-current-datetime: Changes the current date and time on the device. system-restart: Reboots the device. system-shutdown: Shuts down the device. Since this document describes the use of RADIUS for purposes of authentication, it is vulnerable to all of the threats that are present in other RADIUS applications. For a discussion of such threats, see and , and Section 4 of . This document provides configuration parameters for SSH's "publickey" and "password" authentication mechanisms. Section 9.4 of and Section 11 of discuss security considerations for these mechanisms. The "iana&nbhy;crypt&nbhy;hash" YANG module defines a type "crypt&nbhy;hash" that can be used to store MD5 hashes. discusses security considerations for MD5. The usage of MD5 is NOT RECOMMENDED.