Yang data model for TACACS+

This document defines a YANG modules that augment the System data model defined in the with TACACS+ client model. TACACS+ provides Device Administration for routers, network access servers and other networked computing devices via one or more centralized servers which is defined in the TACACS+ Protocol. The System Management Model defines two YANG features to support local or RADIUS authentication: User Authentication Model: Define a list of usernames and passwords and control the order in which local or RADIUS authentication is used. RADIUS Client Model: Defines a list of RADIUS server that a device used. Since TACACS+ is also used for device management and the feature is not contained in the system model, this document defines a YANG data model that allows users to configure TACACS+ client functions on a device for centralized Authentication, Authorization and Accounting provided by TACACS+ servers. The YANG models can be used with network management protocols such as NETCONF to install, manipulate, and delete the configuration of network devices. The YANG data model in this document conforms to the Network Management Datastore Architecture (NMDA) defined in .

The keywords "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 BCP14, , when, and only when, they appear in all capitals, as shown here. The following terms are defined in and are used in this specification: client configuration data server state data The following terms are defined in and are used in this specification: augment data model data node The terminology for describing YANG data models is found in .

Tree diagrams used in this document follow the notation defined in .

This model is used to configure TACACS+ client on the device to support deployment scenarios with centralized authentication, authorization, and accounting servers. Authentication is used to validates a user's name and password, authorization allows the user to access and execute commands at various command levels assigned to the user and accounting keeps track of the activity of a user who has accessed the device. The ietf-system-tacacsplus module is intended to augment the "/sys:system" path defined in the ietf-system module with "tacacsplus" grouping. Therefore, a device can use local, Remote Authentication Dial In User Service (RADIUS), or Terminal Access Controller Access Control System Plus (TACACS+) to validate users who attempt to access the router by several mechanisms, e.g. a command line interface or a web-based user interface. The "server" list is directly under the "tacacsplus" container, which is to hold a list of different TACACS+ server and use server-type to distinguish the three protocols. The list of servers is for redundancy purpose. Most of the parameters in the "server" list are taken directly from the TACACS+ protocol , and some are derived from the wide implementation of network equipment manufacturers. For example, when there are multiple interfaces connected to the TACACS+ server, the source address of outgoing TACACS+ packets could be specified, or the source address could be specified through the interface setting. For the TACACS + server located in a private network, a VRF instance needs to be specified. The "statistics" container under the "server list" is to record session statistics and usage information during user access which include the amount of data a user has sent and/or received during a session. The data model for TACACS+ client has the following structure:

module: ietf-system-tacacsplus augment /sys:system: +--rw tacacsplus {tacacsplus}? +--rw server* [name] +--rw name string +--rw server-type? enumeration +--rw address inet:host +--rw port? inet:port-number +--rw shared-secret string +--rw (source-type)? | +--:(source-ip) | | +--rw source-ip? inet:ip-address | +--:(source-interface) | +--rw source-interface? if:interface-ref +--rw single-connection? boolean +--rw timeout? uint16 +--rw vrf-instance? | -> /ni:network-instances/network-instance/name +--ro statistics +--ro connection-opens? yang:counter64 +--ro connection-closes? yang:counter64 +--ro connection-aborts? yang:counter64 +--ro connection-failures? yang:counter64 +--ro connection-timeouts? yang:counter64 +--ro messages-sent? yang:counter64 +--ro messages-received? yang:counter64 +--ro errors-received? yang:counter64

<CODE BEGINS> file "ietf-system-tacacsplus@2019-06-20.yang"

module ietf-system-tacacsplus { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-system-tacacsplus"; prefix sys-tcsplus; import ietf-inet-types { prefix inet; reference "RFC 6991: Common YANG Data Types"; } import ietf-yang-types { prefix yang; reference "RFC 6991: Common YANG Data Types"; } import ietf-network-instance { prefix ni; reference "RFC 8529: YANG Data Model for Network Instances"; } import ietf-interfaces { prefix if; reference "RFC 8343: A YANG Data Model for Interface Management"; } import ietf-system { prefix sys; reference "RFC 7317: A YANG Data Model for System Management"; } import ietf-netconf-acm { prefix nacm; reference "RFC 8341: Network Configuration Access Control Model"; } organization "IETF Opsawg (Operations and Management Area Working Group)"; contact "WG Web: <http://tools.ietf.org/wg/opsawg/> WG List: <mailto:opsawg@ietf.org> Editor: Guangying Zheng <mailto:zhengguangying@huawei.com>"; description "This module provides configuration of TACACS+ client. 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). This version of this YANG module is part of RFC XXXX; see the RFC itself for full legal notices."; revision 2019-06-20 { description "Initial revision."; reference "foo"; } feature tacacsplus { description "Indicates that the device can be configured as a TACACS+ client."; reference "draft-ietf-opsawg-tacacs-11: The TACACS+ Protocol"; } grouping statistics { description "Grouping for TACACS+ packets statistics attributes"; container statistics { config false; description "A collection of server-related statistics objects"; leaf connection-opens { type yang:counter64; description "Number of new connection requests sent to the server, e.g. socket open"; } leaf connection-closes { type yang:counter64; description "Number of connection close requests sent to the server, e.g. socket close"; } leaf connection-aborts { type yang:counter64; description "Number of aborted connections to the server. These do not include connections that are close gracefully."; } leaf connection-failures { type yang:counter64; description "Number of connection failures to the server"; } leaf connection-timeouts { type yang:counter64; description "Number of connection timeouts to the server"; } leaf messages-sent { type yang:counter64; description "Number of messages sent to the server"; } leaf messages-received { type yang:counter64; description "Number of messages received by the server"; } leaf errors-received { type yang:counter64; description "Number of error messages received from the server"; } } } grouping tacacsplus { description "Grouping for TACACS+ attributes"; container tacacsplus { if-feature "tacacsplus"; description "Container for TACACS+ configurations and operations."; list server { key "name"; ordered-by user; description "List of TACACS+ servers used by the device When the TACACS+ 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 TACACS+ server."; } leaf server-type { type enumeration { enum authentication { description "The server is an authentication server."; } enum authorization { description "The server is an authorization server."; } enum accounting { description "The server is an accounting server."; } } description "Server type: authentication/authorization/accounting."; } leaf address { type inet:host; mandatory true; description "The address of the TACACS+ server."; } leaf port { type inet:port-number; default "49"; description "The port number of TACACS+ Server port."; } leaf shared-secret { type string; mandatory true; nacm:default-deny-all; description "The shared secret, which is known to both the TACACS+ client and server. TACACS+ server administrators SHOULD configure secret keys of minimum 16 characters length."; reference "TACACS+ protocol:"; } choice source-type { description "The source address type for outbound TACACS+ packets."; case source-ip { leaf source-ip { type inet:ip-address; description "Specifies source IP address for TACACS+ outbound packets."; } } case source-interface { leaf source-interface { type if:interface-ref; description "Specifies the interface from which the IP address is derived for use as the source for the outbound TACACS+ packet"; } } } leaf single-connection { type boolean; default "false"; description "Whether the single connection mode is enabled for the server. By default, the single connection mode is disabled."; } leaf timeout { type uint16 { range "1..300"; } units "seconds"; default "5"; description "The number of seconds the device will wait for a response from each TACACS+ server before trying with a different server."; } leaf vrf-instance { type leafref { path "/ni:network-instances/ni:network-instance/ni:name"; } description "Specifies the VPN Routing and Forwarding (VRF) instance to use to communicate with the TACACS+ server."; } uses statistics; } } } augment "/sys:system" { description "Augment the system model with authorization and accounting attributes Augment the system model with the tacacsplus model"; uses tacacsplus; } } <CODE ENDS>

The YANG module defined in this document is designed to be accessed via network management protocols such as NETCONF or RESTCONF . The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH) . The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS . The NETCONF access control model 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. 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 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. This document describes the use of TACACS+ for purposes of authentication, authorization and accounting, it is vulnerable to all of the threats that are present in TACACS+ applications. For a discussion of such threats, see Section 9 of the TACACS+ Protocol.

This document registers a URI in the IETF XML registry . Following the format in , the following registration is requested to be made:

URI: urn:ietf:params:xml:ns:yang:ietf-system-tacacsplus Registrant Contact: The IESG. XML: N/A, the requested URI is an XML namespace. This document registers a YANG module in the YANG Module Names registry .

Name: ietf-system-tacacsplus Namespace: urn:ietf:params:xml:ns:yang: ietf-tacacsplus Prefix: sys-tcsplus Reference: RFC XXXX

The authors wish to thank Alex Campbell and Ebben Aries, Alan DeKok, Joe Clarke, many others for their helpful comments.