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Authentication Order for LDAPS, RADIUS, TACACS+, and Local Password

Junos OS Evolved supports different authentication methods, including local password authentication, RADIUS, and TACACS+ to control access to the network.

Note:

Junos OS Evolved does not support LDAPS.

When you configure a device to support multiple authentication methods, you can prioritize the order in which the device tries the different methods. This topic discusses how the authentication order works and how to configure it on a device.

Authentication Order Overview

You (the network administrator) can configure the authentication-order statement to prioritize the order in which Junos OS Evolved tries different authentication methods to verify user access to a router or switch. If you do not set an authentication order, by default, Junos OS Evolved verifies users based on their configured local passwords.

If the authentication order includes LDAPS, RADIUS, or TACACS+ servers, but the servers do not respond to a request, Junos OS Evolved always defaults to trying local password authentication as a last resort.

If the authentication order includes LDAPS, RADIUS, or TACACS+ servers, but the servers reject the request, the handling of the request is more complicated.

  • If password (local password authentication) is included at the end of the authentication order and the remote authentication servers reject the authentication request, the device attempts local password authentication.

  • If password (local password authentication) is not included in the authentication order and the remote authentication servers reject the authentication request, the request ends with the rejection.

    Note:

    In Junos OS Evolved Release 20.4R1 and earlier releases, if the remote authentication servers reject the request, the device still attempts local password authentication.

Thus, the device must include password as a final authentication order option for the device to attempt local password authentication in the event that the remote authentication servers reject the request.

If the authentication order is set to authentication-order password, then the device uses only local password authentication.

Using Remote Authentication

You can configure Junos OS Evolved to be a RADIUS or TACACS+ authentication client (or both).

Note:

Junos OS Evolved does not support LDAPS.

If an authentication method included in the authentication-order statement is not available, or if the authentication method is available but the corresponding authentication server returns a reject response, Junos OS Evolved tries the next authentication method included in the authentication-order statement.

The LDAP, RADIUS, or TACACS+ server authentication might fail for one or more of the following reasons:

  • The authentication method is configured, but the corresponding authentication servers are not configured. For instance, the RADIUS and TACACS+ authentication methods are included in the authentication-order statement, but the corresponding RADIUS or TACACS+ servers are not configured at the respective [edit system radius-server] and [edit system tacplus-server] hierarchy levels.

  • The authentication server does not respond before the configured timeout value for that server, or before the default timeout, if no timeout is configured.

  • The authentication server is not reachable because of a network problem.

The authentication server might return a reject response for one or both of the following reasons:

  • The user profile of a user accessing a router or switch is not configured on the authentication server.

  • The user enters incorrect logon credentials.

How to Use Local Password Authentication

You can explicitly configure the password authentication method in the authentication-order statement or use this method as a fallback mechanism when remote authentication servers fail. The password authentication method consults the local user profiles configured at the [edit system login] hierarchy level. Users can log in to a router or switch using their local username and password in the following scenarios:

  • The password authentication method (password) is explicitly configured as one of the authentication methods in the authentication-order statement.

    In this case, the device tries local password authentication if no previous authentication method accepts the logon credentials. This is true whether the previous authentication methods fail to respond or they return a reject response because of an incorrect username or password.

  • The password authentication method is not explicitly configured as one of the authentication methods in the authentication-order statement.

    In this case, the operating system only tries local password authentication if all configured authentication methods fail to respond. The operating system does not use local password authentication if any configured authentication method returns a reject response because of an incorrect username or password.

    Note:

    In Junos OS Evolved Release 20.4R1 and earlier releases, Junos OS Evolved still tries local password authentication whether the other authentication methods return a reject response or fail to respond.

Order of Authentication Attempts

Table 1 describes how the authentication-order statement at the [edit system] hierarchy level determines the procedure that Junos OS uses to authenticate users for access to a device.

Table 1: Order of Authentication Attempts

Syntax

Order of Authentication Attempts

authentication-order radius;

  1. Try configured RADIUS authentication servers.

  2. If a RADIUS server is available and authentication is accepted, grant access.

  3. If a RADIUS server is available but authentication is rejected, deny access.

    Note:

    In Junos OS Evolved Release 20.4R1 and earlier releases, if a RADIUS server is available but authentication is rejected, try local password authentication.

  4. If no RADIUS servers are available, try local password authentication.

authentication-order [ radius password ];

  1. Try configured RADIUS authentication servers.

  2. If a RADIUS server is available and authentication is accepted, grant access.

  3. If the RADIUS servers fail to respond or the servers return a reject response, try local password authentication, because it is explicitly configured in the authentication order.

authentication-order [ radius tacplus ];

  1. Try configured RADIUS authentication servers.

  2. If a RADIUS server is available and authentication is accepted, grant access.

  3. If the RADIUS servers fail to respond or the servers return a reject response, try configured TACACS+ servers.

  4. If a TACACS+ server is available and authentication is accepted, grant access.

  5. If a TACACS+ server is available but authentication is rejected, deny access.

    Note:

    In Junos OS Evolved Release 20.4R1 and earlier releases, if a TACACS+ server is available but authentication is rejected, try local password authentication.

  6. If no RADIUS or TACACS+ servers are available, try local password authentication.

authentication-order [ radius tacplus password ];

  1. Try configured RADIUS authentication servers.

  2. If a RADIUS server is available and authentication is accepted, grant access.

  3. If the RADIUS servers fail to respond or the servers return a reject response, try configured TACACS+ servers.

  4. If a TACACS+ server is available and authentication is accepted, grant access.

  5. If the TACACS+ servers fail to respond or the servers return a reject response, try local password authentication, because it is explicitly configured in the authentication order.

authentication-order tacplus;

  1. Try configured TACACS+ authentication servers.

  2. If a TACACS+ server is available and authentication is accepted, grant access.

  3. If a TACACS+ server is available but authentication is rejected, deny access.

    Note:

    In Junos OS Evolved Release 20.4R1 and earlier releases, if a TACACS+ server is available but authentication is rejected, try local password authentication.

  4. If no TACACS+ servers are available, try local password authentication.

authentication-order [ tacplus password ];

  1. Try configured TACACS+ authentication servers.

  2. If a TACACS+ server is available and authentication is accepted, grant access.

  3. If the TACACS+ servers fail to respond or the servers return a reject response, try local password authentication, because it is explicitly configured in the authentication order.

authentication-order [ tacplus radius ];

  1. Try configured TACACS+ authentication servers.

  2. If a TACACS+ server is available and authentication is accepted, grant access.

  3. If the TACACS+ servers fail to respond or the servers return a reject response, try configured RADIUS servers.

  4. If a RADIUS server is available and authentication is accepted, grant access.

  5. If a RADIUS server is available but authentication is rejected, deny access.

    Note:

    In Junos OS Evolved Release 20.4R1 and earlier releases, if a RADIUS server is available but authentication is rejected, try local password authentication.

  6. If no TACACS+ or RADIUS servers are available, try local password authentication.

authentication-order [ tacplus radius password ];

  1. Try configured TACACS+ authentication servers.

  2. If a TACACS+ server is available and authentication is accepted, grant access.

  3. If the TACACS+ servers fail to respond or the servers return a reject response, try configured RADIUS servers.

  4. If a RADIUS server is available and authentication is accepted, grant access.

  5. If the RADIUS servers fail to respond or the servers return a reject response, try local password authentication, because it is explicitly configured in the authentication order.

authentication-order password;

  1. Try to authenticate the user using the password configured at the [edit system login] hierarchy level.

  2. If the authentication is accepted, grant access.

  3. If the authentication is rejected, deny access.

Note:

If SSH public keys are configured, SSH user authentication first tries to perform public key authentication before using the authentication methods configured in the authentication-order statement. If you want SSH logins to use the authentication methods configured in the authentication-order statement without first trying to perform public key authentication, do not configure SSH public keys.

Configure the Authentication Order for LDAPS, RADIUS, TACACS+ and Local Password Authentication

Using the authentication-order statement, you can prioritize the order in which Junos OS Evolved tries the different authentication methods when verifying user access to a router or switch. If you do not set an authentication order, by default, users are verified based on their locally configured passwords.

When configuring a password using plain text and relying on Junos OS Evolved to encrypt it, you are still sending the password over the Internet in plain text. Using pre-encrypted passwords is more secure because it means that the plain text of the password never has to be sent over the internet. Also, with passwords, only one user can be assigned to a password at a time.

On the other hand, LDAPS, RADIUS, and TACACS+ encrypt passwords. These authentication methods let you assign a set of users at a time instead of assigning users one by one. But here are how these authentication systems differ:

  • RADIUS uses UDP; TACACS+ and LDAPS use TCP.

  • RADIUS encrypts only the password during transmission, whereas TACACS+ and LDAPS encrypt the entire session.

  • RADIUS and LDAPS combine authentication (device) and authorization (user), whereas TACACS+ separates authentication, authorization, and accountability.

In short, TACACS+ is more secure than RADIUS. However, RADIUS has better performance and is more interoperable. RADIUS is widely supported, whereas TACACS+ is a Cisco proprietary product and not widely supported outside of Cisco.

LDAPS is more secure than RADIUS and TACACS+, as it relies on a private key mechanism instead of the shared key used in the case of RADIUS and TACACS+. The TLS protocol secures the transmission of data effectively between the LDAP client and the LDAP server.

You can configure the authentication order based on your system, its restrictions, and your IT policy and operational preferences.

To configure the authentication order, include the authentication-order statement at the [edit system] hierarchy level.

For a list of hierarchy levels at which you can include this statement, see the statement summary section for this statement.

The following are the possible authentication order entry options:

  • radius—Verify the user using RADIUS authentication servers.

  • tacplus—Verify the user using TACACS+ authentication servers.

  • password—Verify the user using the username and password configured locally in the authentication statement at the [edit system login user] hierarchy level.

The Challenge Handshake Authentication Protocol (CHAP) authentication sequence cannot take more than 30 seconds. If it takes longer than 30 seconds to authenticate a client, the authentication is abandoned and a new sequence is initiated.

For example, assume that you configure three RADIUS servers so that the router or switch attempts to contact each server three times. Assume further that, with each retry, the server times out after 3 seconds. In this scenario, the maximum time given to the RADIUS authentication method before CHAP considers it a failure is 27 seconds. If you add more RADIUS servers to this configuration, they might not be contacted because the authentication process might be abandoned before these servers are tried.

Junos OS Evolved enforces a limit on the number of standing authentication server requests that the CHAP authentication can have at one time. Thus, an authentication server method—RADIUS, for example—might fail to authenticate a client when this limit is exceeded. If authentication fails, the authentication sequence is reinitiated by the router or switch until authentication succeeds and the link is established. However, if the RADIUS servers are unavailable and additional authentication methods such as tacplus or password are also configured, the next authentication method is tried.

The following example shows how to configure radius and password authentication:

The following example shows how to insert the tacplus statement after the radius statement:

The following example shows how to delete the radius statement from the authentication order:

Example: Configure Authentication Order

This example shows how to configure authentication order for user login.

Requirements

Before you begin, perform the initial device configuration. See the Getting Started Guide for your device.

Overview

You can configure the authentication method order that a device uses to verify user access to the device. For each login attempt, the device tries the authentication methods in the order configured, until the password matches or all authentication methods have been tried. If you do not configure remote authentication, users are verified based on their configured local passwords.

This example configures the device to attempt user authentication with RADIUS authentication services first, then with TACACS+ authentication services, and finally with local password authentication.

When you use local password authentication, you must create a local user account for every user who wants to access the system. However, when you use remote authentication servers, you can create template accounts (for authorization purposes) that a set of users shares. When a user is assigned to a template account, the command-line interface (CLI) username is the login name; however, the user inherits the privileges, file ownership, and effective user ID from the template account.

Configuration

Procedure

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, copy and paste the commands into the CLI at the [edit] hierarchy level, and then enter commit in configuration mode.

Step-by-Step Procedure

To configure authentication order:

  1. Delete any existing authentication-order statement.

  2. Add RADIUS authentication to the authentication order.

  3. Add TACACS+ authentication to the authentication order.

  4. Add local password authentication to the authentication order.

Results

In configuration mode, confirm your configuration by entering the show system authentication-order command. If the output does not display the intended configuration, repeat the configuration instructions in this example to correct it.

After you configure the device, enter commit in configuration mode.

Note:

To completely set up RADIUS or TACACS+ authentication, you must configure at least one RADIUS or TACACS+ server and create user accounts or user template accounts.

Verification

Confirm that the configuration is working properly.

Verify the Authentication Order Configuration

Purpose

Verify that the device uses the authentication methods in the order configured.

Action

Create a test user that has a different password for each authentication method. Log in to the device using the different passwords. Verify that the device queries subsequent authentication methods when the previous methods reject the password or fail to respond.

Alternatively, in a test environment, you can deactivate the authentication server configuration or the local user account configuration (or both) to test each authentication method. For example, to test the TACACS+ server, you can deactivate the RADIUS server configuration and the user's local account. However, if you deactivate the user's local account, you must ensure that the user still maps to a local user template account such as the remote user template.

Release History Table
Release
Description
20.4R1
Starting in Junos OS Evolved Release 20.4R2 and 21.1R1, password authentication behavior is updated to match the password authentication behavior of Junos OS: If the authentication order includes LDAPS, RADIUS, or TACACS+ servers, but the servers do not respond to a request, Junos OS Evolved always defaults to trying local password authentication as a last resort.