A YANG Data Model for Terminal Access Controller Access-Control System Plus (TACACS+)

Design of the TACACS+ Data Model This module is used to configure a TACACS+ client on a device to support deployment scenarios with centralized authentication, authorization, and accounting servers. Authentication is used to validate a user's username and password, authorization allows the user to access and execute commands at various privilege levels assigned to the user, and accounting keeps track of the activity of a user who has accessed the device. The ietf-system-tacacs-plus module augments the "/sys:system" path defined in the ietf-system module with the contents of the "tacacs- plus" grouping. Therefore, a device can use local, RADIUS, or TACACS+ authentication 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, which is directly under the "tacacs-plus" container, holds a list of TACACS+ servers and uses server-type to distinguish between Authentication, Authorization, and Accounting (AAA) services. The list of servers is for redundancy. When there are multiple interfaces connected to the TACACS+ client or server, the source address of outgoing TACACS+ packets could be specified, or the source address could be specified through the interface IP address setting or derived from the outbound interface from the local Forwarding Information Base (FIB). For the TACACS+ server located in a Virtual Private Network (VPN), a VPN Routing and Forwarding (VRF) instance needs to be specified. The "statistics" container under the "server list" is a collection of read-only counters for sent and received messages from a configured server. The YANG module for TACACS+ client has the following structure: /ni:network-instances/network-instance/name +--rw single-connection? boolean +--rw timeout? uint16 +--ro statistics +--ro discontinuity-time yang:date-and-time +--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 +--ro sessions? yang:counter64 +--ro cert-errors? yang:counter64 +--ro rpk-errors? yang:counter64 {tlsc:server-auth-raw-public-key}? ]]> Specifically, the module is designed to cover the following key requirements specified in :

TLS 1.3 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, so that it may be included in the TLS Server Name Indication (SNI) extension.

The following new data nodes are supported compared to :

'client-credentials' and 'server-credentials':: Defines a set credentials that can be globally provisioned and then referenced under specific servers.
'domain-name':: Provides a domain name of the server per .
'sni-enabled':: Controls activation of Server Name Indication (SNI) (). This paramter can be used only if a domain name is provided.
'client-identity':: Specifies the identity credentials that the client may present when establishing a connection to a server. Client identities can be configured at the top level and then referenced for specific server instances. Alternatively, client identities can be configured explicitely under each server instance.
'server-authentication':: Specifies how a client authenticates servers. Server credentials can be configured at the top level and then referenced for specific server instances. Alternatively, client identities can be configured explicitely under each server instance.
'hello-params':: Controls TLS versions and cipher suites.
'keepalives':: Providers a set of parameters for testing the aliveness of the server.
'discontinuity-time':: The time on the most recent occasion at which the client suffered a discontinuity.
'cert-errors':: Number of connection failures due to certificate issues.
'rpk-errors':: Number of RPK-related connection failures.

TACACS+ Client Module This module uses types and groupings defined in , , , , , , , and . The module augments . The module also cites , , , and . WG List: Editor: Mohamed Boucadair Author: Bo Wu Author: Guangying Zheng "; description "This module provides configuration of TACACS+ clients. 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 (RFC 2119) (RFC 8174) when, and only when, they appear in all capitals, as shown here. 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 XXXX; see the RFC itself for full legal notices."; revision 2024-12-11 { description "This revision adds TLS support"; reference "RFC XXXX: A YANG Model for Terminal Access Controller Access-Control System Plus (TACACS+)"; } revision 2021-08-05 { description "Initial revision."; reference "RFC 9105: A YANG Data Model for Terminal Access Controller Access-Control System Plus (TACACS+)"; } feature credential-reference { description "Indicates whether service credentials references are supported."; } identity tacacs-plus { base sys:authentication-method; description "Indicates AAA operation using TACACS+."; } typedef tacacs-plus-server-type { type bits { bit authentication { description "Indicates that the TACACS+ server is providing authentication services."; } bit authorization { description "Indicates that the TACACS+ server is providing authorization services."; } bit accounting { description "Indicates that the TACACS+ server is providing accounting services."; } } description "tacacs-plus-server-type can be set to authentication/authorization/accounting or any combination of the three types."; } typedef client-credentials-ref { type leafref { path "/sys:system/sys-tcs-plus:tacacs-plus" + "/sys-tcs-plus:client-credentials/sys-tcs-plus:id"; } description "Defines a type to reference client credentials."; } typedef server-credentials-ref { type leafref { path "/sys:system/sys-tcs-plus:tacacs-plus" + "/sys-tcs-plus:server-credentials/sys-tcs-plus:id"; } description "Defines a type to reference server credentials."; } grouping base-statistics { description "Grouping for TACACS+ statistics attributes."; 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 closed 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 from the server."; } leaf errors-received { type yang:counter64; description "Number of error messages received from the server."; } leaf sessions { type yang:counter64; description "Number of TACACS+ sessions completed with the server. If the Single Connection Mode was not enabled, the number of sessions is the same as the number of 'connection-closes'. If the Single Connection Mode was enabled, a single TCP connection may contain multiple TACACS+ sessions."; } } grouping statistics { description "Grouping for TACACS+ statistics attributes."; leaf discontinuity-time { type yang:date-and-time; mandatory true; description "The time on the most recent occasion at which the TACACS+ client suffered a discontinuity."; } uses base-statistics; leaf cert-errors { type yang:counter64; description "Number of connection failures due to certificate issues."; } leaf rpk-errors { if-feature "tlsc:server-auth-raw-public-key"; type yang:counter64; description "Number of RPK-related connection failures."; } } grouping certificate { description "Specifies the client identity using a certificate."; uses "ks:inline-or-keystore-end-entity-cert-with-key-" + "grouping" { refine "inline-or-keystore/inline/inline-definition" { must 'not(public-key-format) or derived-from-or-self' + '(public-key-format, "ct:subject-public-key-' + 'info-format")'; } refine "inline-or-keystore/central-keystore/" + "central-keystore-reference/asymmetric-key" { must 'not(deref(.)/../ks:public-key-format) or ' + 'derived-from-or-self(deref(.)/../ks:public-' + 'key-format, "ct:subject-public-key-info-' + 'format")'; } } } grouping raw-private-key { description "Specifies the client identity using a raw private key."; uses ks:inline-or-keystore-asymmetric-key-grouping { refine "inline-or-keystore/inline/inline-definition" { must 'not(public-key-format) or derived-from-or-self' + '(public-key-format, "ct:subject-public-key-' + 'info-format")'; } refine "inline-or-keystore/central-keystore/" + "central-keystore-reference" { must 'not(deref(.)/../ks:public-key-format) or ' + 'derived-from-or-self(deref(.)/../ks:public-' + 'key-format, "ct:subject-public-key-info-format")'; } } } grouping tls13-epsk { description "An External Pre-Shared Key (EPSK) is established or provisioned out-of-band, i.e., not from a TLS connection. An EPSK is a tuple of (Base Key, External Identity, Hash). When PSKs are provisioned out of band, the PSK identity and the Key Derivation Function (KDF) hash algorithm to be used with the PSK must also be provisioned."; reference "RFC 8446: The Transport Layer Security (TLS) Protocol Version 1.3, Section 4.2.11 RFC 9257: Guidance for External Pre-Shared Key (PSK) Usage in TLS, Section 6 RFC 9258: Importing External Pre-Shared Keys (PSKs) for TLS 1.3, Section 5.1"; uses ks:inline-or-keystore-symmetric-key-grouping; leaf external-identity { type string; mandatory true; description "A sequence of bytes used to identify an EPSK. A label for a pre-shared key established externally."; reference "RFC 8446: The Transport Layer Security (TLS) Protocol Version 1.3, Section 4.2.11 RFC 9257: Guidance for External Pre-Shared Key (PSK) Usage in TLS, Section 4.1"; } leaf hash { type tlscmn:epsk-supported-hash; default "sha-256"; description "For externally established PSKs, the Hash algorithm must be set when the PSK is established or default to SHA-256 if no such algorithm is defined."; reference "RFC 8446: The Transport Layer Security (TLS) Protocol Version 1.3, Section 4.2.11"; } leaf context { type string; description "The context used to determine the EPSK, if any exists. For example, context may include information about peer roles or identities to mitigate Selfie-style reflection attacks."; reference "RFC 9258: Importing External Pre-Shared Keys (PSKs) for TLS 1.3, Section 5.1 "; } leaf target-protocol { type uint16; description "Specifies the protocol for which a PSK is imported for use."; reference "RFC 9258: Importing External Pre-Shared Keys (PSKs) for TLS 1.3, Section 3 "; } leaf target-kdf { type uint16; description "The KDF for which a PSK is imported for use."; reference "RFC 9258: Importing External Pre-Shared Keys (PSKs) for TLS 1.3, Section 3"; } } grouping client-identity { description "Identity credentials that the TLS client may present when establishing a connection to a TLS server. When configured, and requested by the TLS server when establishing a TLS session, these credentials are passed in the Certificate message."; reference "RFC 8446: The Transport Layer Security (TLS) Protocol Version 1.3, Section 4.4.2"; nacm:default-deny-write; choice auth-type { //default "certificate"; //mandatory true; description "A choice amongst authentication types, of which one must be enabled and selected."; case certificate { container certificate { description "Specifies the client identity using a certificate."; uses certificate; } } case raw-public-key { if-feature "tlsc:client-ident-raw-public-key"; container raw-private-key { description "Specifies the client identity using RPK."; uses raw-private-key; } } case tls13-epsk { if-feature "tlsc:client-ident-tls13-epsk"; container tls13-epsk { description "An EPSK is established or provisioned out-of-band."; uses tls13-epsk; } } } } grouping client-identity-with-ref { description "Identity credentials that the TLS client may present when establishing a connection to a TLS server. When configured, and requested by the TLS server when establishing a TLS session, these credentials are passed in the Certificate message."; choice ref-or-explicit { description "A choice between a reference of explicit configuration."; case ref { description "Provides a reference."; leaf credentials-reference { if-feature credential-reference; type sys-tcs-plus:client-credentials-ref; description "Specifies the client credentials reference."; } } case explicit { description "Explicit configuration."; uses client-identity; } } } grouping server-authentication { description "Specifies how the TLS client can authenticate TLS servers. Any combination of credentials is additive and unordered."; nacm:default-deny-write; container ca-certs { presence "Indicates that Certification Authority (CA) certificates have been configured. This statement is present so the mandatory descendant nodes do not imply that this node must be configured."; description "A set of CA certificates used by the TLS client to authenticate TLS server certificates. A server certificate is authenticated if it has a valid chain of trust to a configured CA certificate."; reference "RFC 9641: A YANG Data Model for a Truststore"; uses ts:inline-or-truststore-certs-grouping; } container ee-certs { presence "Indicates that End Entity (EE) certificates have been configured. This statement is present so the mandatory descendant nodes do not imply that this node must be configured."; description "A set of server certificates (i.e., end entity certificates) used by the TLS client to authenticate certificates presented by TLS servers. A server certificate is authenticated if it is an exact match to a configured server certificate."; reference "RFC 9641: A YANG Data Model for a Truststore"; uses ts:inline-or-truststore-certs-grouping; } container raw-public-keys { if-feature "tlsc:server-auth-raw-public-key"; presence "Indicates that raw public keys have been configured. This statement is present so the mandatory descendant nodes do not imply that this node must be configured."; description "A set of raw public keys used by the TLS client to authenticate raw public keys presented by the TLS server. A raw public key is authenticated if it is an exact match to a configured raw public key."; reference "RFC 9641: A YANG Data Model for a Truststore"; uses ts:inline-or-truststore-public-keys-grouping { refine "inline-or-truststore/inline/inline-definition/" + "public-key" { must 'derived-from-or-self(public-key-format,' + ' "ct:subject-public-key-info-format")'; } refine "inline-or-truststore/central-truststore/" + "central-truststore-reference" { must 'not(deref(.)/../ts:public-key/ts:public-key-' + 'format[not(derived-from-or-self(., "ct:subject-' + 'public-key-info-format"))])'; } } } leaf tls13-epsks { if-feature "tlsc:server-auth-tls13-epsk"; type empty; description "Indicates that the TLS client can authenticate TLS servers using configured external PSKs."; } } grouping server-authentication-with-ref { description "Specifies how the TLS client can authenticate TLS servers."; choice ref-or-explicit { description "A choice between a reference of explicit configuration."; case ref { description "Provides a reference."; leaf credentials-reference { if-feature credential-reference; type sys-tcs-plus:server-credentials-ref; description "Specifies the server credentials reference."; } } case explicit { description "Explicit configuration."; uses server-authentication; } } } grouping hello-params { description "Configurable parameters for the TLS hello message."; nacm:default-deny-write; uses tlscmn:hello-params-grouping { refine "tls-versions/min" { must "not(derived-from-or-self(current(), " + "'tlscmn:tls12'))" { error-message "TLS 1.2 is not supported as min TLS version"; } } refine "tls-versions/max" { must "not(derived-from-or-self(current(), " + "'tlscmn:tls12'))" { error-message "TLS 1.2 is not supported as max TLS version"; } } } } grouping tls-client { description "A grouping for configuring a TLS client without any consideration for how an underlying TCP session is established."; container client-identity { presence "Indicates that a TLS-level client identity has been configured. This statement is present so the mandatory descendant do not imply that this node must be configured."; description "Identity credentials the TLS client may present when establishing a connection to a TLS server."; //uses client-identity; uses client-identity-with-ref; } container server-authentication { must 'ca-certs or ee-certs or raw-public-keys or tls13-epsks'; description "Specifies how the TLS client can authenticate TLS servers."; //uses server-authentication; uses server-authentication-with-ref; } container hello-params { if-feature "tlscmn:hello-params"; description "Configurable parameters for the TLS hello message."; uses hello-params; } } grouping tls-grouping-reuse { description "A grouping for TLS with TLS1.2 and keepalive removed."; uses tlsc:tls-client-grouping { refine "client-identity/auth-type/tls12-psk" { if-feature "not tlsc:client-ident-tls12-psk"; } refine "server-authentication/tls12-psks" { if-feature "not tlsc:server-auth-tls12-psk"; } refine "hello-params/tls-versions/min" { must "not(derived-from-or-self(current(), " + "'tlscmn:tls12'))" { error-message "TLS 1.2 is not supported as min TLS version"; } } refine "hello-params/tls-versions/max" { must "not(derived-from-or-self(current(), " + "'tlscmn:tls12'))" { error-message "TLS 1.2 is not supported as max TLS version"; } } refine "keepalives" { if-feature "not tlsc:tls-client-keepalives"; } } } grouping tacacs-plus { description "Grouping for TACACS+ attributes."; container tacacs-plus { must "not(derived-from-or-self(../sys:authentication" + "/sys:user-authentication-order, 'tacacs-plus'))" + " or bit-is-set(server/server-type,'authentication')" { error-message "When 'tacacs-plus' is used as a system authentication method, a TACACS+ authentication server must be configured."; description "When 'tacacs-plus' is used as an authentication method, a TACACS+ server must be configured."; } description "Container for TACACS+ configurations and operations."; list client-credentials { if-feature credential-reference; key "id"; description "Identity credentials the TLS client may present when establishing a connection to a TLS server. A list of client credentials to be referenced."; nacm:default-deny-write; leaf id { type string; description "A credential identifier."; } uses client-identity; } list server-credentials { if-feature credential-reference; key "id"; description "Identity credentials the TLS client may present when establishing a connection to a TLS server."; nacm:default-deny-write; leaf id { type string; description "A credential identifier."; } uses server-authentication; } list server { key "name"; ordered-by user; description "List of TACACS+ servers used by the device."; leaf name { type string; description "An arbitrary name for the TACACS+ server."; } leaf server-type { type tacacs-plus-server-type; mandatory true; description "Server type: authentication/authorization/accounting and various combinations."; } leaf domain-name { type inet:domain-name; description "Provides a domain name of the TACACS+ server."; } leaf sni-enabled { type boolean; must '../domain-name' { error-message "A domain name must be provided to make use of Server Name Indication (SNI)."; } description "Enables the use of SNI, when set to true. Disables the use of SNI, when set to false."; reference "RFC 6066: Transport Layer Security (TLS) Extensions: Extension Definitions, Section 3"; } leaf address { type inet:host; mandatory true; description "The address of the TACACS+ server."; } leaf port { type inet:port-number; default "49"; // to be replaced by TACACS-TLS-PORT description "The port number of TACACS+ Sserver port number."; } choice security { mandatory true; //default "tls"; description "Security mechanism between TACACS+ client and server."; case tls { description "TLS is used."; uses tls-client; //uses client-identity-with-ref; } case obfuscation { leaf shared-secret { type string { length "1..max"; } description "The shared secret, which is known to both the TACACS+ client and server. TACACS+ server administrators SHOULD configure a shared secret with a minimum length of 16 characters. It is highly recommended that this shared secret is at least 32 characters long and sufficiently complex with a mix of different character types, i.e., upper case, lower case, numeric, and punctuation. Note that this security mechanism is best described as 'obfuscation' and not 'encryption' as it does not provide any meaningful integrity, privacy, or replay protection."; reference "RFC 8907: The TACACS+ Protocol"; nacm:default-deny-all; } } } choice source-type { description "The source address type for outbound TACACS+ packets."; case source-ip { leaf source-ip { type inet:ip-address; description "Specifies the 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 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."; reference "RFC 8529: YANG Data Model for Network Instances"; } leaf single-connection { type boolean; default "false"; description "Indicates whether the Single Connection Mode is enabled for the server. By default, the Single Connection Mode is disabled."; } leaf timeout { type uint16 { range "1..max"; } 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."; } uses statistics; } } } augment "/sys:system" { description "Augments the system model with the tacacs-plus model."; uses tacacs-plus; } } ]]>