A YANG Model for Terminal Access Controller Access-Control System Plus (TACACS+) over TLS 1.3

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Table of Contents

1. Introduction

[RFC9105] defines a YANG module ("ietf-system-tacacs-plus") that augments the System Management data model defined in [RFC7317] for the management of Terminal Access Controller Access-Control System Plus (TACACS+) clients. Typically, the "ietf-system-tacacs-plus" module is used to configure a TACACS+ client on a device to support deployment scenarios with centralized authentication, authorization, and accounting servers.¶

This document defines a YANG module for managing TACACS+ over TLS 1.3 clients [I-D.ietf-opsawg-tacacs-tls13]. The module is designed as an augmentation to the "ietf-system-tacacs-plus" module specified in [RFC9105].¶

• Discussion Note: RFC 9105bis or keep the current augment design.¶

The module leverages the TLS structures defined in [I-D.ietf-netconf-tls-client-server]. Concretely, this first version of the specification uses a pruning approach rather that a reuse of the groupings defined in [I-D.ietf-netconf-tls-client-server].¶

2. Conventions and Definitions

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.¶

The meanings of the symbols in the YANG tree diagrams are defined in [RFC8340].¶

The document uses the terms defined in Section 2 of [I-D.ietf-opsawg-tacacs-tls13] and Section 3 of [RFC8907].¶

'client' refers to TLS TACACS+ client, while 'server' refers to TLS TACACS+ server.¶

• Note to the RFC Editor: Please update the following:¶

  • AAAA --> the assigned RFC number for [I-D.ietf-netconf-crypto-types]¶

  • BBBB --> the assigned RFC number for [I-D.ietf-netconf-trust-anchors]¶

  • CCCC --> the assigned RFC number for [I-D.ietf-netconf-keystore]¶

  • FFFF --> the assigned RFC number for [I-D.ietf-netconf-tls-client-server]¶

  • XXXX --> the assigned RFC number for this document.¶

3. Module Tree Structure

The module is designed to cover the following key requirements specified in [I-D.ietf-opsawg-tacacs-tls13]:¶

• TLS 1.3 [RFC8446] MUST be used for transport.¶

• Earlier TLS versions TLS MUST NOT be used.¶

• The cipher suites offered or accepted SHOULD be configurable.¶

• Implementations MAY support Raw Public Keys and PSK.¶

• Implementations MUST support the ability to configure the server's domain name¶

The abstract tree structure is shown below:¶

{::include-fold ./trees/tree-overview.txt}

The following data nodes are supported:¶

'client-credentials' and 'server-credentials':

Defines a set credentials that can be globally provisioned and then referenced under specific servers.¶

'remote-address':

Specifies a list of IP address/port numbers that can be used to reach a server instance.¶

A server instance may be identified by an IPv4 address, IPv6 address, or both.¶

One or multiple addresses of the same address family may be provided.¶

The same or distinct port numbers may be used per address family.¶

This container takes precedence over "address" and "port" data nodes defined in [RFC9105].¶

'domain-name':

Provides a domain name of the server per Section 3.3 of [I-D.ietf-opsawg-tacacs-tls13].¶

'client-identity':

Specifies the identity credentials that the client may present when establishing a connection to a server. Both explicit and reference are supported.¶

'server-authentication':

Specifies how a client authenticates servers. Both explicit and reference are supported.¶

'hello-params':

Controls TLS versions and cipher suites.¶

'keepalives':

Providers a set of parameters for testing the aliveness of the server.¶

4. YANG Module

This module uses types and groupings defined in [RFC6991], [RFC8341], [I-D.ietf-netconf-crypto-types], [I-D.ietf-netconf-trust-anchors], [I-D.ietf-netconf-keystore], and [I-D.ietf-netconf-tls-client-server].¶

The module augments [RFC9105], which is also an augment of [RFC7317].¶

The module also cites [RFC9257], [RFC9258], [RFC9258], and [RFC6520].¶

<CODE BEGINS> file "ietf-system-secure-tacacs@2024-05-23.yang"

{::include-fold ./yang/ietf-system-secure-tacacs.yang}

<CODE ENDS>

5. Security Considerations

This section uses the template described in Section 3.7 of [I-D.ietf-netmod-rfc8407bis].¶

The YANG module specified in this document defines schema for data that is designed to be accessed via network management protocols such as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS [RFC8446].¶

The Network Configuration Access Control Model (NACM) [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.¶

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) and delete operations to these data nodes without proper protection or authentication can have a negative effect on network operations. Specifically, the following subtrees and data nodes have particular sensitivities/vulnerabilities:¶

 'xxx':
 :  xxxx.

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. Specifically, the following subtrees and data nodes have particular sensitivities/vulnerabilities:¶

 'xxx':
 :  xxxx.

This YANG module uses groupings from other YANG modules that define nodes that may be considered sensitive or vulnerable in network environments. Refer to Section 5.3 of [I-D.ietf-netconf-tls-client-server] for information as to which nodes may be considered sensitive or vulnerable in network environments.¶

6. IANA Considerations

IANA is requested to register the following URI in the "ns" subregistry within the "IETF XML Registry" [RFC3688]:¶

   URI:  urn:ietf:params:xml:ns:yang:ietf-system-secure-tacacs
   Registrant Contact:  The IESG.
   XML:  N/A; the requested URI is an XML namespace.

IANA is requested to register the following YANG module in the "YANG Module Names" registry [RFC6020] within the "YANG Parameters" registry group:¶

   Name:  ietf-system-secure-tacacs
   Namespace:  urn:ietf:params:xml:ns:yang:ietf-system-secure-tacacs
   Prefix:  secure-tacacs
   Maintained by IANA?  N
   Reference:  RFC XXXX

7. References

Appendix A. Full Tree

The full tree structure is shown below:¶

{::include-fold ./trees/full-tree.txt}

Acknowledgments

The document leverages data structures defined in [I-D.ietf-netconf-tls-client-server].¶

Thanks to Bo Wu for the review and comments.¶

Author's Address