CLI Book 1: Cisco ASA Series General Operations CLI Configuration Guide, 9.2

Licensing Requirements for ASA Access for ASDM, Telnet, or SSH

The following table shows the licensing requirements for this feature:

Guidelines and Limitations

This section includes the guidelines and limitations for this feature.

Context Mode Guidelines

Supported in single and multiple context mode.

Firewall Mode Guidelines

Supported in routed and transparent firewall mode.

IPv6 Guidelines

Supports IPv6.

Model Guidelines

For the ASASM, a session from the switch to the ASASM is a Telnet session, but Telnet access configuration according to this section is not required.

Additional Guidelines

• You cannot use Telnet to the lowest security interface unless you use Telnet inside a VPN tunnel.
• Management access to an interface other than the one from which you entered the ASA is not supported. For example, if your management host is located on the outside interface, you can only initiate a management connection directly to the outside interface. The only exception to this rule is through a VPN connection. See Configuring Management Access Over a VPN Tunnel.
• The ASA allows:

– A maximum of 5 concurrent Telnet connections per context, if available, with a maximum of 100 connections divided among all contexts.

– A maximum of 5 concurrent SSH connections per context, if available, with a maximum of 100 connections divided among all contexts.

– A maximum of 5 concurrent ASDM instances per context, if available, with a maximum of 32 ASDM instances among all contexts.

• The ASA supports the SSH remote shell functionality provided in SSH Versions 1 and 2 and supports DES and 3DES ciphers.
• XML management over SSL and SSH is not supported.
• (8.4 and later) The SSH default username is no longer supported. You can no longer connect to the ASA using SSH with the pix or asa username and the login password. To use SSH, you must configure AAA authentication using the aaa authentication ssh console LOCAL command; then define a local user by entering the username command. If you want to use a AAA server for authentication instead of the local database, we recommend also configuring local authentication as a backup method.
• (9.1(2) and later) The default Telnet login password was removed; you must manually set the password before using Telnet. See Configuring the Hostname, Domain Name, and Passwords.
• If you cannot make a Telnet or SSH connection to the ASA interface, make sure that you enabled Telnet or SSH to the ASA according to the instructions in the Configuring ASA Access for ASDM, Telnet, or SSH.
• The AES-CTR encryption for SSH supports only AES-128 on single-core platforms, which includes the ASA 5505.

a.

Configuring Telnet Access

To identify the client IP addresses allowed to connect to the ASA using Telnet, perform the following steps.

Detailed Steps

Examples

The following example shows how to let a host on the inside interface with an address of 192.168.1.2 access the ASA:

The following example shows how to allow all users on the 192.168.3.0 network to access the ASA on the inside interface:

Using a Telnet Client

To gain access to the ASA CLI using Telnet, enter the login password set by the password command. You must manually set the password before using Telnet. See Configuring the Hostname, Domain Name, and Passwords.

If you configure Telnet authentication (see Configuring Authentication for CLI and ASDM Access), then enter the username and password defined by the AAA server or local database.

Configuring SSH Access

To identify the client IP addresses and define a user allowed to connect to the ASA using SSH, perform the following steps:

Detailed Steps

Examples

The following example shows how to generate RSA keys and let a host on the inside interface with an address of 192.168.1.2 access the ASA:

The following example shows how to allow all users on the 192.168.3.0/24 network to access the ASA on the inside interface:

Using an SSH Client

In the SSH client on your management host, enter the username and password that you configured in the Configuring SSH Access. When starting an SSH session, a dot (.) displays on the ASA console before the following SSH user authentication prompt appears:

The display of the dot does not affect the functionality of SSH. The dot appears at the console when generating a server key or decrypting a message using private keys during SSH key exchange before user authentication occurs. These tasks can take up to two minutes or longer. The dot is a progress indicator that verifies that the ASA is busy and has not hung.

You can alternatively configure a public key instead of using a password. See Adding a User Account to the Local Database.

Configuring HTTPS Access for ASDM

To use ASDM, you need to enable the HTTPS server, and allow HTTPS connections to the ASA. HTTPS access is enabled as part of the factory default configuration or when you use the setup command. This section describes how to manually configure ASDM access.

Detailed Steps

Examples

The following example shows how to enable the HTTPS server and let a host on the inside interface with an address of 192.168.1.2 access ASDM:

The following example shows how to allow all users on the 192.168.3.0/24 network to access ASDM on the inside interface:

Licensing Requirements for CLI Parameters

Guidelines and Limitations

This section includes the guidelines and limitations for this feature.

Context Mode Guidelines

Supported in single and multiple context mode.

Firewall Mode Guidelines

Supported in routed and transparent firewall mode.

Configuring a Login Banner

You can configure a message to display when a user connects to the ASA, before a user logs in, or before a user enters privileged EXEC mode.

Restrictions

After a banner is added, Telnet or SSH sessions to ASA may close if:

• There is not enough system memory available to process the banner message(s).
• A TCP write error occurs when trying to display banner message(s).

Guidelines

• From a security perspective, it is important that your banner discourage unauthorized access. Do not use the words “welcome” or “please,” as they appear to invite intruders in. The following banner sets the correct tone for unauthorized access:

• See RFC 2196 for guidelines about banner messages.

To configure a login banner, perform the following steps:

Detailed Steps

Examples

The following example shows how to add a message-of-the-day banner:

Customizing a CLI Prompt

The CLI Prompt pane lets you customize the prompt used during CLI sessions. By default, the prompt shows the hostname of the ASA. In multiple context mode, the prompt also displays the context name. You can display the following items in the CLI prompt:

Detailed Steps

To customize the CLI prompt, enter the following commands:

Changing the Console Timeout

The console timeout sets how long a connection can remain in privileged EXEC mode or configuration mode; when the timeout is reached, the session drops into user EXEC mode. By default, the session does not time out. This setting does not affect how long you can remain connected to the console port, which never times out.

To change the console timeout, perform the following steps:

Detailed Steps

Information About ICMP Access

ICMP in IPv6 functions the same as ICMP in IPv4. ICMPv6 generates error messages, such as ICMP destination unreachable messages and informational messages like ICMP echo request and reply messages. Additionally ICMP packets in IPv6 are used in the IPv6 neighbor discovery process and path MTU discovery.

We recommend that you always grant permission for the ICMP unreachable message type (type 3). Denying ICMP unreachable messages disables ICMP path MTU discovery, which can halt IPsec and PPTP traffic. See RFC 1195 and RFC 1435 for details about path MTU discovery.

If you configure ICMP rules, then the ASA uses a first match to the ICMP traffic followed by an implicit deny all entry. That is, if the first matched entry is a permit entry, the ICMP packet continues to be processed. If the first matched entry is a deny entry or an entry is not matched, the ASA discards the ICMP packet and generates a syslog message. An exception is when an ICMP rule is not configured; in that case, a permit statement is assumed.

Licensing Requirements for ICMP Access

Guidelines and Limitations

This section includes the guidelines and limitations for this feature.

Context Mode Guidelines

Supported in single and multiple context mode.

Firewall Mode Guidelines

Supported in routed and transparent firewall mode.

IPv6 Guidelines

Supports IPv6.

Additional Guidelines

• The ASA does not respond to ICMP echo requests directed to a broadcast address.
• The ASA only responds to ICMP traffic sent to the interface that traffic comes in on; you cannot send ICMP traffic through an interface to a far interface.
• If you cannot ping the ASA interface, make sure that you enable ICMP to the ASA for your IP address using the icmp command.

Default Settings

By default, you can send ICMP packets to any ASA interface using either IPv4 or IPv6.

Configuring ICMP Access

To configure ICMP access rules, enter one of the following commands:

Detailed Steps

Examples

The following example shows how to allow all hosts except the one at 10.1.1.15 to use ICMP to the inside interface:

The following example shows how to allow the host at 10.1.1.15 to use only ping to the inside interface, enter the following command:

The following example shows how to deny all ping requests and permit all packet-too-big messages (to support path MTU discovery) at the outside interface:

The following example shows how to permit host 2000:0:0:4::2 or hosts on prefix 2001::/64 to ping the outside interface:

Licensing Requirements for a Management Interface

Guidelines and Limitations

This section includes the guidelines and limitations for this feature.

Context Mode Guidelines

Supported in single mode.

Firewall Mode Guidelines

Supported in routed mode.

IPv6 Guidelines

Supports IPv6.

Additional Guidelines

You can define only one management access interface.

Note For the configurations that follow, 192.168.10.0/24 is the VPN pool for AnyConnect or IPsec VPN clients. Each configuration allows VPN client users to connect to ASDM or SSH to the ASA using the management interface IP address.

To allow only VPN client users access to ASDM or HTTP (and deny access to all other users), enter the following commands:

To allow only VPN client users access to the ASA using SSH (and deny access to all other users), enter the following command:

Configuring a Management Interface

To configure the management interface, perform the following steps.

Detailed Steps

Information About AAA for System Administrators

This section describes AAA for system administrators and includes the following topics:

• Information About Management Authentication
• Information About Command Authorization

Information About Management Authentication

This section describes authentication for management access and includes the following topics:

• Comparing CLI Access with and without Authentication
• Comparing ASDM Access with and without Authentication
• Authenticating Sessions from the Switch to the ASA Services Module

Comparing CLI Access with and without Authentication

How you log into the ASA depends on whether or not you enable authentication:

• No Authentication—If you do not enable any authentication for Telnet, you do not enter a username; you enter the login password (set with the password command). (SSH is not available without authentication). You access user EXEC mode.
• Authentication—If you enable Telnet or SSH authentication according to this section, you enter the username and password as defined on the AAA server or local user database. You access user EXEC mode.

To enter privileged EXEC mode after logging in, enter the enable command. How enable works depends on whether you enable authentication:

• No Authentication—If you do not configure enable authentication, enter the system enable password when you enter the enable command (set by the enable password command). However, if you do not use enable authentication, after you enter the enable command, you are no longer logged in as a particular user. To maintain your username, use enable authentication.
• Authentication—If you configure enable authentication (see Configuring Authentication to Access Privileged EXEC Mode (the enable Command)), the ASA prompts you for your username and password again. This feature is particularly useful when you perform command authorization, in which usernames are important in determining the commands that a user can enter.

For enable authentication using the local database, you can use the login command instead of the enable command. login maintains the username but requires no configuration to turn on authentication. See Authenticating Users with the login Command for more information.

Comparing ASDM Access with and without Authentication

By default, you can log into ASDM with a blank username and the enable password set by the enable password command. Note that if you enter a username and password at the login screen (instead of leaving the username blank), ASDM checks the local database for a match.

If you configure HTTP authentication, you can no longer use ASDM with a blank username and the enable password.

Authenticating Sessions from the Switch to the ASA Services Module

For sessions from the switch to the ASASM (using the session command), you can configure Telnet authentication. For virtual console connections from the switch to the ASASM (using the service-module session command), you can configure serial port authentication.

In multiple context mode, you cannot configure any AAA commands in the system configuration. However, if you configure Telnet or serial authentication in the admin context, then authentication also applies to sessions from the switch to the ASASM. The admin context AAA server or local user database is used in this instance.

Information About Command Authorization

This section describes command authorization and includes the following topics:

• Supported Command Authorization Methods
• About Preserving User Credentials
• Security Contexts and Command Authorization

Supported Command Authorization Methods

You can use one of two command authorization methods:

• Local privilege levels—Configure the command privilege levels on the ASA. When a local, RADIUS, or LDAP (if you map LDAP attributes to RADIUS attributes) user authenticates for CLI access, the ASA places that user in the privilege level that is defined by the local database, RADIUS, or LDAP server. The user can access commands at the assigned privilege level and below. Note that all users access user EXEC mode when they first log in (commands at level 0 or 1). The user needs to authenticate again with the enable command to access privileged EXEC mode (commands at level 2 or higher), or they can log in with the login command (local database only).

Note You can use local command authorization without any users in the local database and without CLI or enable authentication. Instead, when you enter the enable command, you enter the system enable password, and the ASA places you in level 15. You can then create enable passwords for every level, so that when you enter enable n (2 to 15), the ASA places you in level n. These levels are not used unless you enable local command authorization (see Configuring Local Command Authorization). (See the command reference for more information about the enable command.)

• TACACS+ server privilege levels—On the TACACS+ server, configure the commands that a user or group can use after authenticating for CLI access. Every command that a user enters at the CLI is validated with the TACACS+ server.

About Preserving User Credentials

When a user logs into the ASA, that user is required to provide a username and password for authentication. The ASA retains these session credentials in case further authentication is needed later in the session.

When the following configurations are in place, a user needs only to authenticate with the local server for login. Subsequent serial authorization uses the saved credentials. The user is also prompted for the privilege level 15 password. When exiting privileged mode, the user is authenticated again. User credentials are not retained in privileged mode.

• The local server is configured to authenticate user access.
• Privilege level 15 command access is configured to require a password.
• The user account is configured for serial-only authorization (no access to console or ASDM).
• The user account is configured for privilege level 15 command access.

The following table shows how credentials are used in this case by the ASA.

Security Contexts and Command Authorization

The following are important points to consider when implementing command authorization with multiple security contexts:

• AAA settings are discrete per context, not shared among contexts.

When configuring command authorization, you must configure each security context separately. This configuration provides you the opportunity to enforce different command authorizations for different security contexts.

When switching between security contexts, administrators should be aware that the commands permitted for the username specified when they login may be different in the new context session or that command authorization may not be configured at all in the new context. Failure to understand that command authorizations may differ between security contexts could confuse an administrator. This behavior is further complicated by the next point.

• New context sessions started with the changeto command always use the default enable_15 username as the administrator identity, regardless of which username was used in the previous context session. This behavior can lead to confusion if command authorization is not configured for the enable_15 user or if authorizations are different for the enable_15 user than for the user in the previous context session.

This behavior also affects command accounting, which is useful only if you can accurately associate each command that is issued with a particular administrator. Because all administrators with permission to use the changeto command can use the enable_15 username in other contexts, command accounting records may not readily identify who was logged in as the enable_15 username. If you use different accounting servers for each context, tracking who was using the enable_15 username requires correlating the data from several servers.

When configuring command authorization, consider the following:

• An administrator with permission to use the changeto command effectively has permission to use all commands permitted to the enable_15 user in each of the other contexts.
• If you intend to authorize commands differently per context, ensure that in each context the enable_15 username is denied use of commands that are also denied to administrators who are permitted use of the changeto command.

When switching between security contexts, administrators can exit privileged EXEC mode and enter the enable command again to use the username that they need.

Note The system execution space does not support AAA commands; therefore, command authorization is not available in the system execution space.

Licensing Requirements for AAA for System Administrators

Prerequisites

Prerequisites for the AAA Server or Local Database

You must configure users in a AAA server or the local database. For a AAA server, you then need to configure the ASA to communicate with it. See the following chapters:

• AAA server—See the applicable AAA server-type chapter.
• Local Database—See Adding a User Account to the Local Database.

Prerequisites for Management Authentication

Before the ASA can authenticate a Telnet, SSH, or HTTP user, you must identify the IP addresses that are allowed to communicate with the ASA. For the ASASM, the exception is for access to the system in multiple context mode; a session from the switch to the ASASM is a Telnet session, but Telnet access configuration is not required. For more information, see Configuring ASA Access for ASDM, Telnet, or SSH.

Prerequisites for Local Command Authorization

• Configure enable authentication. (See Configuring Authentication for CLI and ASDM Access.)

enable authentication is essential for maintaining the username after the user accesses the enable command.

Alternatively, you can use the login command (which is the same as the enable command with authentication; for the local database only), which requires no configuration. We do not recommend this option because it is not as secure as enable authentication.

You can also use CLI authentication, but it is not required.

• See the following prerequisites for each user type:

– Local database users—Configure each user in the local database at a privilege level from 0 to 15.

– RADIUS users—Configure the user with Cisco VSA CVPN3000-Privilege-Level with a value between 0 and 15.

– LDAP users—Configure the user with a privilege level between 0 and 15, and then map the LDAP attribute to Cisco VSA CVPN3000-Privilege-Level according to the Configuring LDAP Attribute Maps.

Prerequisites for TACACS+ Command Authorization

• Configure CLI authentication (see Configuring Authentication for CLI and ASDM Access).
• Configure enable authentication (see Configuring Authentication to Access Privileged EXEC Mode (the enable Command)).

Prerequisites for Management Accounting

• Configure CLI authentication (see Configuring Authentication for CLI and ASDM Access).
• Configure enable authentication (see Configuring Authentication to Access Privileged EXEC Mode (the enable Command)).

Guidelines and Limitations

This section includes the guidelines and limitations for this feature.

Context Mode Guidelines

Supported in single and multiple context mode.

Firewall Mode Guidelines

Supported in routed and transparent firewall mode.

IPv6 Guidelines

Supports IPv6.

Default Settings

Default Command Privilege Levels

By default, the following commands are assigned to privilege level 0. All other commands are assigned to privilege level 15.

• show checksum
• show curpriv
• enable
• help
• show history
• login
• logout
• pager
• show pager
• clear pager
• quit
• show version

If you move any configure mode commands to a lower level than 15, be sure to move the configure command to that level as well, otherwise, the user will not be able to enter configuration mode.

To view all privilege levels, see Viewing Local Command Privilege Levels.

Configuring Authentication for CLI and ASDM Access

You can require authentication for CLI, ASDM, and enable command access.

Prerequisites

• Configure Telnet, SSH, or HTTP access according to the Configuring ASA Access for ASDM, Telnet, or SSH.
• For SSH access, you must configure SSH authentication; there is no default username.

Detailed Steps

Configuring Authentication to Access Privileged EXEC Mode (the enable Command)

You can configure the ASA to authenticate users with a AAA server or the local database when they enter the enable command. Alternatively, users are automatically authenticated with the local database when they enter the login command, which also accesses privileged EXEC mode depending on the user level in the local database.

This section includes the following topics:

• Configuring Authentication for the enable Command
• Authenticating Users with the login Command

Configuring Authentication for the enable Command

You can configure the ASA to authenticate users when they enter the enable command. See Comparing CLI Access with and without Authentication for more information.

To authenticate users who enter the enable command, enter the following command.

Authenticating Users with the login Command

From user EXEC mode, you can log in as any username in the local database using the login command.

This feature allows users to log in with their own username and password to access privileged EXEC mode, so you do not have to provide the system enable password to everyone. To allow users to access privileged EXEC mode (and all commands) when they log in, set the user privilege level to 2 (the default) through 15. If you configure local command authorization, then the user can only enter commands assigned to that privilege level or lower. See Configuring Local Command Authorization for more information.

Caution If you add users to the local database who can gain access to the CLI and whom you do not want to enter privileged EXEC mode, you should configure command authorization. Without command authorization, users can access privileged EXEC mode (and all commands) at the CLI using their own password if their privilege level is 2 or greater (2 is the default). Alternatively, you can use a AAA server for authentication, or you can set all local users to level 1 so you can control who can use the system enable password to access privileged EXEC mode.

---

To log in as a user from the local database, enter the following command:

Limiting User CLI and ASDM Access with Management Authorization

The ASA enables you to distinguish between administrative and remote-access users when they authenticate using RADIUS, LDAP, TACACS+, or the local user database. User role differentiation can prevent remote access VPN and network access users from establishing an administrative connection to the ASA.

Note Serial access is not included in management authorization, so if you configure the aaa authentication serial consolecommand, then any user who authenticates can access the console port.

Detailed Steps

Step 1 To enable management authorization for local, RADIUS, LDAP (mapped), and TACACS+ users, enter the following command:

ciscoasa(config)# aaa authorization exec { authentication-server | LOCAL } [ auto-enable ]

When the LOCAL option is configured, the local user database is the source for the username entered and the Service-Type and Privilege-Level attributes assigned.

This option also enables support of administrative user privilege levels from RADIUS, which can be used in conjunction with local command privilege levels for command authorization. See Configuring Local Command Authorization for more information.

When the authentication-server option is configured, the same server is used for both authentication and authorization.

The auto-enable option allows users with sufficient privileges from the login authentication server to be placed directly in privileged EXEC mode. Otherwise, users are placed in user EXEC mode. These privileges are determined by the Service-Type and Privilege-Level attributes that are required to enter each EXEC mode. To enter privileged EXEC mode, users must have a Service-Type attribute of Administrative and a Privilege Level attribute of greater than 1 assigned to them.

This option is not supported in the system context. However, if you configure Telnet or serial authentication in the admin context, then authentication also applies to sessions from the switch to the ASASM.

There is no effect if you enter the aaa authorization exec command alone.

The auto-enable option is not included when you use serial authentication in management authorization.

The aaa authentication http command is not affected by the auto-enable option.

Before you configure the auto-enable option, we recommend that you configure both protocol login and enable authentication, and that all authentication requests go to the same AAA server group, as shown in the following example:

We do not recommend that you use other types of configurations.

Step 2 To configure the user for management authorization, see the following requirements for each AAA server type or local user:

RADIUS or LDAP (mapped) users

When users are authenticated through LDAP, the native LDAP attributes and their values can be mapped to Cisco ASA attributes to provide specific authorization features. Configure Cisco VSA CVPN3000-Privilege-Level with a value between 0 and 15. and then map the LDAP attributes to Cisco VAS CVPN3000-Privilege-Level using the ldap map-attributes command. For more information, see Configuring LDAP Attribute Maps.

The RADIUS IETF service-type attribute, when sent in an access-accept message as the result of a RADIUS authentication and authorization request, is used to designate which type of service is granted to the authenticated user:

• Service-Type 6 (Administrative)—Allows full access to any services specified by the aaa authentication console commands.
• Service-Type 7 (NAS prompt)—Allows access to the CLI when you configure the aaa authentication { telnet | ssh} console command, but denies ASDM configuration access if you configure the aaa authentication http console command. ASDM monitoring access is allowed. If you configure enable authentication with the aaa authentication enable console command, the user cannot access privileged EXEC mode using the enable command. The Framed (2) and Login (1) service types are treated the same way.
• Service-Type 5 (Outbound)—Denies management access. The user cannot use any services specified by the aaa authentication console commands(excluding the serial keyword; serial access is allowed). Remote access (IPsec and SSL) users can still authenticate and terminate their remote access sessions. All other service types (Voice, FAX, and so on) are treated the same way.

The RADIUS Cisco VSA privilege-level attribute (Vendor ID 3076, sub-ID 220), when sent in an access-accept message, is used to designate the level of privilege for the user.

When an authenticated user tries administrative access to the ASA through ASDM, SSH, or Telnet, but does not have the appropriate privilege level to do so, the ASA generates syslog message 113021. This message informs the user that the attempted login failed because of inappropriate administrative privileges.

The following example shows how to define an LDAP attribute map. In this example, the security policy specifies that users being authenticated through LDAP map the user record fields or parameters title and company to the IETF-RADIUS service-type and privilege-level, respectively.

The following example applies an LDAP attribute map to an LDAP AAA server:

TACACS+ users

Authorization is requested with “service=shell,” and the server responds with PASS or FAIL.

• PASS, privilege level 1—Allows access to ASDM, with limited read-only access to the configuration and monitoring sections, and access for show commands that are privilege level 1 only.
• PASS, privilege level 2 and higher—Allows access to the CLI when you configure the aaa authentication { telnet | ssh} console command, but denies ASDM configuration access if you configure the aaa authentication http console command. ASDM monitoring access is allowed. If you configure enable authentication with the aaa authentication enable console command, the user cannot access privileged EXEC mode using the enable command. You are not allowed to access privileged EXEC mode using the enable command if your enable privilege level is set to 14 or less.
• FAIL—Denies management access. You cannot use any services specified by the aaa authentication console commands(excluding the serial keyword; serial access is allowed).

Local users

Set the service-type command for a given username. By default, the service-type is admin, which allows full access to any services specified by the aaa authentication console command. For more information, see Adding a User Account to the Local Database.

Configuring a Password Policy for Local Database Users

When you configure authentication for CLI or ASDM access using the local database, you can configure a password policy that requires a user to change their password after a specified amount of time and also requires password standards such as a minimum length and the minimum number of changed characters.

The password policy only applies to administrative users using the local database, and not to other types of traffic that can use the local database, such as VPN or AAA for network access, and not to users authenticated by a AAA server.

This section includes the following topics:

• Configuring the Password Policy
• Changing Your Password

Configuring the Password Policy

After you configure the password policy, when you change a password (either your own or another user’s), the password policy applies to the new password. Any existing passwords are grandfathered in. The new policy applies to changing the password with the username command as well as the change-password command.

Prerequisites

• Configure CLI/ASDM authentication according to the Configuring Authentication for CLI and ASDM Access. Be sure to specify the local database.
• Configure enable authentication according to the Configuring Authentication to Access Privileged EXEC Mode (the enable Command). Be sure to specify the local database.

Detailed Steps

Changing Your Password

If you configure a password lifetime in the password policy, you need to change your username password to a new one when the old password expires. This password change method is required if you enable password policy authentication (the password-policy authenticate enable command). If password policy authentication is not enabled, then you can use this method, or you can change your user account directly with the username command.

Detailed Steps

Configuring Command Authorization

If you want to control access to commands, the ASA lets you configure command authorization, where you can determine which commands that are available to a user. By default when you log in, you can access user EXEC mode, which offers only minimal commands. When you enter the enable command (or the login command when you use the local database), you can access privileged EXEC mode and advanced commands, including configuration commands.

You can use one of two command authorization methods:

• Local privilege levels
• TACACS+ server privilege levels

For more information about command authorization, see Information About Command Authorization.

This section includes the following topics:

• Configuring Local Command Authorization
• Viewing Local Command Privilege Levels
• Configuring Commands on the TACACS+ Server
• Configuring TACACS+ Command Authorization

Configuring Local Command Authorization

Local command authorization lets you assign commands to one of 16 privilege levels (0 to 15). By default, each command is assigned either to privilege level 0 or 15. You can define each user to be at a specific privilege level, and each user can enter any command at the assigned privilege level or below. The ASA supports user privilege levels defined in the local database, a RADIUS server, or an LDAP server (if you map LDAP attributes to RADIUS attributes). See the following sections for more information:

• Adding a User Account to the Local Database
• Supported Authentication Methods
• Configuring LDAP Attribute Maps

To configure local command authorization, perform the following steps:

Detailed Steps

Examples

The filter command has the following forms:

• filter (represented by the configure option)
• show running-config filter
• clear configure filter

You can set the privilege level separately for each form, or set the same privilege level for all forms by omitting this option. The following example shows how to set each form separately:

Alternatively, the following example shows how to set all filter commands to the same level:

The show privilege command separates the forms in the display.

The following example shows the use of the mode keyword. The enable command must be entered from user EXEC mode, while the enable password command, which is accessible in configuration mode, requires the highest privilege level:

The following example shows an additional command, the configure command, which uses the mode keyword:

Note This last line is for the configure terminal command.

Viewing Local Command Privilege Levels

The following commandslet you view privilege levels for commands.

Examples

For the show running-config all privilege all command, the ASA displays the current assignment of each CLI command to a privilege level. The following is sample output from this command:

The following example shows the command assignments for privilege level 10:

The following example shows the command assignments for the access-list command:

Configuring Commands on the TACACS+ Server

You can configure commands on a Cisco Secure Access Control Server (ACS) TACACS+ server as a shared profile component, for a group, or for individual users. For third-party TACACS+ servers, see your server documentation for more information about command authorization support.

See the following guidelines for configuring commands in Cisco Secure ACS Version 3.1; many of these guidelines also apply to third-party servers:

• The ASA sends the commands to be authorized as shell commands, so configure the commands on the TACACS+ server as shell commands.

Note Cisco Secure ACS might include a command type called “pix-shell.” Do not use this type for ASA command authorization.

• The first word of the command is considered to be the main command. All additional words are considered to be arguments, which need to be preceded by permit or deny.

For example, to allow the show running-configuration aaa-server command, add show running-configuration to the command field, and type permit aaa-server in the arguments field.

• You can permit all arguments of a command that you do not explicitly deny by checking the Permit Unmatched Args check box.

For example, you can configure just the show command, then all the show commands are allowed. We recommend using this method so that you do not have to anticipate every variant of a command, including abbreviations and a question mark, which shows CLI usage.

• For commands that are a single word, you must permit unmatched arguments, even if there are no arguments for the command, for example enable or help.
• To disallow some arguments, enter the arguments preceded by deny.

For example, to allow enable, but not enable password, enter enable in the commands field, and deny password in the arguments field. Be sure to check the Permit Unmatched Args check box so that enable alone is still allowed.

• When you abbreviate a command at the command line, the ASA expands the prefix and main command to the full text, but it sends additional arguments to the TACACS+ server as you enter them.

For example, if you enter sh log, then the ASA sends the entire command to the TACACS+ server, show logging. However, if you enter sh log mess, then the ASA sends show logging mess to the TACACS+ server, and not the expanded command show logging message. You can configure multiple spellings of the same argument to anticipate abbreviations.

• We recommend that you allow the following basic commands for all users:

– show checksum

– show curpriv

– enable

– help

– show history

– login

– logout

– pager

– show pager

– clear pager

– quit

– show version

Configuring TACACS+ Command Authorization

If you enable TACACS+ command authorization, and a user enters a command at the CLI, the ASA sends the command and username to the TACACS+ server to determine if the command is authorized.

Before you enable TACACS+ command authorization, be sure that you are logged into the ASA as a user that is defined on the TACACS+ server, and that you have the necessary command authorization to continue configuring the ASA. For example, you should log in as an admin user with all commands authorized. Otherwise, you could become unintentionally locked out.

Do not save your configuration until you are sure that it works the way you want. If you get locked out because of a mistake, you can usually recover access by restarting the ASA. If you still get locked out, see Recovering from a Lockout.

Be sure that your TACACS+ system is completely stable and reliable. The necessary level of reliability typically requires that you have a fully redundant TACACS+ server system and fully redundant connectivity to the ASA. For example, in your TACACS+ server pool, include one server connected to interface 1, and another to interface 2. You can also configure local command authorization as a fallback method if the TACACS+ server is unavailable. In this case, you need to configure local users and command privilege levels according to procedures listed in the Configuring Command Authorization.

To configure TACACS+ command authorization, enter the following command:

Detailed Steps

Configuring Management Access Accounting

You can send accounting messages to the TACACS+ accounting server when you enter any command other than show commands at the CLI. You can configure accounting when users log in, when they enter the enable command, or when they issue commands.

For command accounting, you can only use TACACS+ servers.

To configure management access and enable command accounting, perform the following steps:

Detailed Steps

Viewing the Currently Logged-In User

To view the current logged-in user, enter the following command:

Examples

The following is sample output from the show curpriv command:

Table 43-1 describes the show curpriv command output.

Setting a Management Session Quota

You can establish a maximum number of simultaneous management sessions. If the maximum is reached, no additional sessions are allowed and a syslog message is generated. To prevent a system lockout, the management session quota mechanism cannot block a console session.

To set a management session quota, enter the following command:

Exchanging Keys in an SSH Session

The Diffie-Hellman (DH) key exchange provides a shared secret that cannot be determined by either party alone. The key exchange is combined with a signature and the host key to provide host authentication. This key-exchange method provides explicit server authentication.

Both the DH Group 1 and Group 14 key-exchange methods for key exchange are supported on the ASA. If no DH group key-exchange method is specified, the DH group 1 key-exchange method is used. For more information about using DH key-exchange methods, see RFC 4253.

To exchange keys in an SSH session, enter the following command:

Recovering from a Lockout

In some circumstances, when you turn on command authorization or CLI authentication, you can be locked out of the ASA CLI. You can usually recover access by restarting the ASA. However, if you already saved your configuration, you might be locked out. Table 43-2 lists the common lockout conditions and how you might recover from them.