draft-ietf-opsawg-tacacs-yang-10.txt   draft-ietf-opsawg-tacacs-yang-11.txt 
Opsawg B. Wu, Ed. Opsawg B. Wu, Ed.
Internet-Draft G. Zheng Internet-Draft G. Zheng
Intended status: Standards Track M. Wang, Ed. Intended status: Standards Track M. Wang, Ed.
Expires: October 10, 2021 Huawei Expires: October 28, 2021 Huawei
April 8, 2021 April 26, 2021
A YANG Module for TACACS+ A YANG Module for TACACS+
draft-ietf-opsawg-tacacs-yang-10 draft-ietf-opsawg-tacacs-yang-11
Abstract Abstract
This document defines a Terminal Access Controller Access-Control This document defines a Terminal Access Controller Access-Control
System Plus (TACACS+) client YANG module, that augments the System System Plus (TACACS+) client YANG module, that augments the System
Management data model, defined in RFC 7317, to allow devices to make Management data model, defined in RFC 7317, to allow devices to make
use of TACACS+ servers for centralized Authentication, Authorization use of TACACS+ servers for centralized Authentication, Authorization
and Accounting (AAA). and Accounting (AAA). Though being a standard module, this module
does not endorse the security mechanisms of the TACACS+ protocol (RFC
8907) and TACACS+ MUST be used within a secure deployment.
The YANG module in this document conforms to the Network Management The YANG module in this document conforms to the Network Management
Datastore Architecture (NMDA) defined in RFC 8342. Datastore Architecture (NMDA) defined in RFC 8342.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 10, 2021. This Internet-Draft will expire on October 28, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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o User Authentication Model: Defines a list of usernames with o User Authentication Model: Defines a list of usernames with
associated passwords and a configuration leaf to decide the order associated passwords and a configuration leaf to decide the order
in which local or RADIUS authentication is used. in which local or RADIUS authentication is used.
o RADIUS Client Model: Defines a list of RADIUS servers used by a o RADIUS Client Model: Defines a list of RADIUS servers used by a
device for centralized user authentication. device for centralized user authentication.
The System Management Model is augmented with the TACACS+ YANG module The System Management Model is augmented with the TACACS+ YANG module
defined in this document to allow the use of TACACS+ servers as an defined in this document to allow the use of TACACS+ servers as an
alternative to RADIUS servers or local user configuration. alternative to RADIUS servers.
The YANG module can be used with network management protocols such as The YANG module can be used with network management protocols such as
NETCONF[RFC6241]. NETCONF[RFC6241].
The YANG module in this document conforms to the Network Management The YANG module in this document conforms to the Network Management
Datastore Architecture (NMDA) defined in [RFC8342]. Datastore Architecture (NMDA) defined in [RFC8342].
2. Conventions used in this document 2. Conventions used in this document
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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o data model o data model
o data node o data node
The terminology for describing YANG data models is found in The terminology for describing YANG data models is found in
[RFC7950]. [RFC7950].
2.1. Tree Diagrams 2.1. Tree Diagrams
Tree diagrams used in this document follow the notation defined in The tree diagram used in this document follows the notation defined
[RFC8340]. in [RFC8340].
3. Design of the TACACS+ Data Model 3. Design of the TACACS+ Data Model
This module is used to configure TACACS+ client on a device to This module is used to configure a TACACS+ client on a device to
support deployment scenarios with centralized authentication, support deployment scenarios with centralized authentication,
authorization, and accounting servers. Authentication is used to authorization, and accounting servers. Authentication is used to
validate a user's username and password, authorization allows the validate a user's username and password, authorization allows the
user to access and execute commands at various command levels user to access and execute commands at various privilege levels
assigned to the user, and accounting keeps track of the activity of a assigned to the user, and accounting keeps track of the activity of a
user who has accessed the device. user who has accessed the device.
The ietf-system-tacacs-plus module augments the "/sys:system" path The ietf-system-tacacs-plus module augments the "/sys:system" path
defined in the ietf-system module with the contents of the"tacacs- defined in the ietf-system module with the contents of the "tacacs-
plus" grouping. Therefore, a device can use local, RADIUS, or plus" grouping. Therefore, a device can use local, RADIUS, or
TACACS+ to validate users who attempt to access the router by several TACACS+ to validate users who attempt to access the router by several
mechanisms, e.g., a command line interface or a web-based user mechanisms, e.g., a command line interface or a web-based user
interface. interface.
The "server" list is directly under the "tacacs-plus" container, The "server" list is directly under the "tacacs-plus" container,
which holds a list of TACACS+ servers and uses server-type to which holds a list of TACACS+ servers and uses server-type to
distinguish between Authentication, Authorization and Accounting distinguish between Authentication, Authorization and Accounting
(AAA). The list of servers is for redundancy. (AAA). The list of servers is for redundancy.
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read-only counters for sent and received messages from a configured read-only counters for sent and received messages from a configured
server. server.
The YANG module for TACACS+ client has the following structure: The YANG module for TACACS+ client has the following structure:
module: ietf-system-tacacs-plus module: ietf-system-tacacs-plus
augment /sys:system: augment /sys:system:
+--rw tacacs-plus +--rw tacacs-plus
+--rw server* [name] +--rw server* [name]
+--rw name string +--rw name string
+--rw server-type? tacacs-plus-server-type +--rw server-type tacacs-plus-server-type
+--rw address inet:host +--rw address inet:host
+--rw port? inet:port-number +--rw port? inet:port-number
+--rw (encryption) +--rw (security)
| +--:(shared-secret) | +--:(obfuscation)
| +--rw shared-secret? string | +--rw shared-secret? string
+--rw (source-type)? +--rw (source-type)?
| +--:(source-ip) | +--:(source-ip)
| | +--rw source-ip? inet:ip-address | | +--rw source-ip? inet:ip-address
| +--:(source-interface) | +--:(source-interface)
| +--rw source-interface? if:interface-ref | +--rw source-interface? if:interface-ref
+--rw vrf-instance? +--rw vrf-instance?
| -> /ni:network-instances/network-instance/name | -> /ni:network-instances/network-instance/name
+--rw single-connection? boolean +--rw single-connection? boolean
+--rw timeout? uint16 +--rw timeout? uint16
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+--ro errors-received? yang:counter64 +--ro errors-received? yang:counter64
+--ro sessions? yang:counter64 +--ro sessions? yang:counter64
4. TACACS+ Client Module 4. TACACS+ Client Module
This YANG module imports typedefs from [RFC6991]. This module also This YANG module imports typedefs from [RFC6991]. This module also
uses the interface typedef from [RFC8343], the leafref to VRF uses the interface typedef from [RFC8343], the leafref to VRF
instance from [RFC8529], and the "default-deny-all" extension instance from [RFC8529], and the "default-deny-all" extension
statement from [RFC8341]. statement from [RFC8341].
<CODE BEGINS> file "ietf-system-tacacs-plus@2021-04-08.yang" <CODE BEGINS> file "ietf-system-tacacs-plus@2021-04-27.yang"
module ietf-system-tacacs-plus { module ietf-system-tacacs-plus {
yang-version 1.1; yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-system-tacacs-plus"; namespace "urn:ietf:params:xml:ns:yang:ietf-system-tacacs-plus";
prefix sys-tcs-plus; prefix sys-tcs-plus;
import ietf-inet-types { import ietf-inet-types {
prefix inet; prefix inet;
reference reference
"RFC 6991: Common YANG Data Types"; "RFC 6991: Common YANG Data Types";
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Copyright (c) 2021 IETF Trust and the persons identified as Copyright (c) 2021 IETF Trust and the persons identified as
authors of the code. All rights reserved. authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents Relating to IETF Documents
(http://trustee.ietf.org/license-info). (http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see the This version of this YANG module is part of RFC XXXX; see the
RFC itself for full legal notices."; RFC itself for full legal notices.";
// RFC Ed.: update the date below with the date of RFC // RFC Ed.: update the date below with the date of RFC
// publication and remove this note. // publication and remove this note.
// RFC Ed.: replace XXXX with actual RFC number and remove // RFC Ed.: replace XXXX with actual RFC number and remove
// this note. // this note.
revision 2021-04-08 { revision 2021-04-27 {
description description
"Initial revision."; "Initial revision.";
reference reference
"RFC XXXX: A YANG Module for TACACS+"; "RFC XXXX: A YANG Module for TACACS+";
} }
typedef tacacs-plus-server-type { typedef tacacs-plus-server-type {
type bits { type bits {
bit authentication { bit authentication {
description description
"Indicates that the TACACS server is providing authentication "Indicates that the TACACS+ server is providing authentication
services."; services.";
} }
bit authorization { bit authorization {
description description
"Indicates that the TACACS server is providing authorization "Indicates that the TACACS+ server is providing authorization
services."; services.";
} }
bit accounting { bit accounting {
description description
"Indicates that the TACACS server is providing accounting "Indicates that the TACACS+ server is providing accounting
services."; services.";
} }
} }
description description
"tacacs-plus-server-type can be set to "tacacs-plus-server-type can be set to
authentication/authorization/accounting authentication/authorization/accounting
or any combination of the three types."; or any combination of the three types.";
} }
identity tacacs-plus { identity tacacs-plus {
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leaf connection-closes { leaf connection-closes {
type yang:counter64; type yang:counter64;
description description
"Number of connection close requests sent to the server, e.g., "Number of connection close requests sent to the server, e.g.,
socket close"; socket close";
} }
leaf connection-aborts { leaf connection-aborts {
type yang:counter64; type yang:counter64;
description description
"Number of aborted connections to the server. These do "Number of aborted connections to the server. These do
not include connections that are close gracefully."; not include connections that are closed gracefully.";
} }
leaf connection-failures { leaf connection-failures {
type yang:counter64; type yang:counter64;
description description
"Number of connection failures to the server"; "Number of connection failures to the server";
} }
leaf connection-timeouts { leaf connection-timeouts {
type yang:counter64; type yang:counter64;
description description
"Number of connection timeouts to the server"; "Number of connection timeouts to the server";
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ordered-by user; ordered-by user;
description description
"List of TACACS+ servers used by the device."; "List of TACACS+ servers used by the device.";
leaf name { leaf name {
type string; type string;
description description
"An arbitrary name for the TACACS+ server."; "An arbitrary name for the TACACS+ server.";
} }
leaf server-type { leaf server-type {
type tacacs-plus-server-type; type tacacs-plus-server-type;
mandatory true;
description description
"Server type: authentication/authorization/accounting and "Server type: authentication/authorization/accounting and
various combinations."; various combinations.";
} }
leaf address { leaf address {
type inet:host; type inet:host;
mandatory true; mandatory true;
description description
"The address of the TACACS+ server."; "The address of the TACACS+ server.";
} }
leaf port { leaf port {
type inet:port-number; type inet:port-number;
default "49"; default "49";
description description
"The port number of TACACS+ Server port."; "The port number of TACACS+ Server port.";
} }
choice encryption { choice security {
mandatory true; mandatory true;
description description
"Encryption mechanism between TACACS+ client and server."; "Security mechanism between TACACS+ client and server.
case shared-secret { Because replacing the mandatory 'shared-secret' with
a future encryption mechanism will result in a
non-backwards-compatible change, the purpose of
this 'security' choice is that new encryption
mechanism could be augmented in as another choice.
Note: The use of leaf 'shared-secret' does not
provide encryption mechanism which is instead obfuscating
the TACACS+ packet payload.";
case obfuscation {
leaf shared-secret { leaf shared-secret {
type string { type string {
length "16..max"; length "1..max";
} }
nacm:default-deny-all; nacm:default-deny-all;
description description
"The shared secret, which is known to both the "The shared secret, which is known to both the
TACACS+ client and server. TACACS+ server TACACS+ client and server. TACACS+ server
administrators should configure shared secret of administrators SHOULD configure a shared secret of
minimum 16 characters length. minimum 16 characters length.
It is highly recommended that this shared secret is It is highly recommended that this shared secret is
at least 32 characters long and sufficiently complex at least 32 characters long and sufficiently complex
with a mix of different character types with a mix of different character types
i.e. upper case, lower case, numeric, punctuation."; i.e. upper case, lower case, numeric, punctuation.";
reference reference
"RFC 8907: The TACACS+ Protocol"; "RFC 8907: The TACACS+ Protocol";
} }
} }
} }
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leaf single-connection { leaf single-connection {
type boolean; type boolean;
default "false"; default "false";
description description
"Whether the single connection mode is enabled for the "Whether the single connection mode is enabled for the
server. By default, the single connection mode is server. By default, the single connection mode is
disabled."; disabled.";
} }
leaf timeout { leaf timeout {
type uint16 { type uint16 {
range "1..300"; range "1..max";
} }
units "seconds"; units "seconds";
default "5"; default "5";
description description
"The number of seconds the device will wait for a "The number of seconds the device will wait for a
response from each TACACS+ server before trying with a response from each TACACS+ server before trying with a
different server."; different server.";
} }
uses statistics; uses statistics;
} }
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There are a number of data nodes defined in this YANG module that are There are a number of data nodes defined in this YANG module that are
writable/creatable/deletable (i.e., config true, which is the writable/creatable/deletable (i.e., config true, which is the
default). These data nodes may be considered sensitive or vulnerable default). These data nodes may be considered sensitive or vulnerable
in some network environments. Write operations (e.g., edit-config) in some network environments. Write operations (e.g., edit-config)
to these data nodes without proper protection can have a negative to these data nodes without proper protection can have a negative
effect on network operations. These are the subtrees and data nodes effect on network operations. These are the subtrees and data nodes
and their sensitivity/vulnerability: and their sensitivity/vulnerability:
/system/tacacsplus/server: This list contains the data nodes used to /system/tacacsplus/server: This list contains the data nodes used to
control the TACACS+ servers used by the device. Unauthorized control the TACACS+ servers used by the device. Unauthorized
access to this list could cause a complete control over the device access to this list could enable an attacker to assume complete
by pointing to a compromised TACACS+ server. control over the device by pointing to a compromised TACACS+
server ,or to modify the counters to hide attacks against the
device.
/system/tacacsplus/server/shared-secret: This leaf controls the key /system/tacacsplus/server/shared-secret: This leaf controls the key
known to both the TACACS+ client and server. Unauthorized access known to both the TACACS+ client and server. Unauthorized access
to this leaf could make the device vulnerable to attacks, to this leaf could make the device vulnerable to attacks,
therefore has been restricted using the "default-deny-all" access therefore it has been restricted using the "default-deny-all"
control defined in [RFC8341]. When setting, it is highly access control defined in [RFC8341]. When setting, it is highly
recommended that the leaf is at least 32 characters long and recommended that the leaf is at least 32 characters long and
sufficiently complex with a mix of different character types i.e. sufficiently complex with a mix of different character types i.e.
upper case, lower case, numeric, punctuation. upper case, lower case, numeric, punctuation.
This document describes the use of TACACS+ for purposes of This document describes the use of TACACS+ for purposes of
authentication, authorization and accounting, it is vulnerable to all authentication, authorization and accounting, it is vulnerable to all
of the threats that are present in TACACS+ applications. For a of the threats that are present in TACACS+ applications. For a
discussion of such threats, see Section 9 of the TACACS+ Protocol discussion of such threats, see Section 10 of the TACACS+ Protocol
[RFC8907]. [RFC8907].
6. IANA Considerations 6. IANA Considerations
This document registers a URI in the IETF XML registry [RFC3688]. This document registers a URI in the IETF XML registry [RFC3688].
Following the format in [RFC3688], the following registration is Following the format in [RFC3688], the following registration is
requested to be made: requested to be made:
URI: urn:ietf:params:xml:ns:yang:ietf-system-tacacs-plus URI: urn:ietf:params:xml:ns:yang:ietf-system-tacacs-plus
Registrant Contact: The IESG. Registrant Contact: The IESG.
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