Cisco ASA 5500 Series Configuration Guide using ASDM, 6.3
Configuring Management Access
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Configuring Management Access

Table Of Contents

Configuring Management Access

Configuring Device Access for ASDM, Telnet, or SSH   

Configuring Management Access

Using an SSH Client

Configuring CLI Parameters

Configuring a Login Banner

Customizing a CLI Prompt

Changing the Console Timeout Period

Configuring File Access

Configuring the FTP Client Mode

Configuring the Adaptive Security Appliance as a Secure Copy Server   

Configuring the Adaptive Security Appliance as a TFTP Client

Adding Mount Points   

Adding a CIFS Mount Point

Adding an FTP Mount Point

Configuring ICMP Access

Configuring Management Access Over a VPN Tunnel

Configuring AAA for System Administrators

Configuring Authentication for CLI, ASDM, and enable command Access

Limiting User CLI and ASDM Access with Management Authorization

Configuring Command Authorization

Command Authorization Overview

Configuring Local Command Authorization

Configuring TACACS+ Command Authorization

Configuring Management Access Accounting

Viewing the Current Logged-In User

Recovering from a Lockout


Configuring Management Access


This chapter describes how to access the adaptive security appliance for system management through Telnet, SSH, and HTTPS (using ASDM). It also describes how to authenticate and authorize users and how to create login banners.

This chapter includes the following sections:

Configuring Device Access for ASDM, Telnet, or SSH

Configuring CLI Parameters

Configuring File Access

Configuring ICMP Access

Configuring Management Access Over a VPN Tunnel

Configuring AAA for System Administrators


Note To access the adaptive security appliance interface for management access, you do not also need an access rule allowing the host IP address. You only need to configure management access according to the sections in this chapter.

To configure the management IP address for transparent firewall mode, see the "Setting the Management IP Address for a Transparent Firewall" section.


Configuring Device Access for ASDM, Telnet, or SSH   

This section describes how to allow clients to access the device using ASDM, Telnet, or SSH, and includes the following topics:

Configuring Management Access

Using an SSH Client

Configuring Management Access

You can manage the adaptive security appliance using ASDM, Telnet, or SSH.

SSH is an application running on top of a reliable transport layer, such as TCP/IP, that provides strong authentication and encryption capabilities.

Restrictions

You cannot use Telnet to the lowest security interface unless you use Telnet inside an IPsec tunnel.

The adaptive security appliance allows :

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

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

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

The adaptive security appliance supports the SSH remote shell functionality provided in SSH Versions 1 and 2 and supports DES and 3DES ciphers.


Note XML management over SSL and SSH is not supported.

In addition, management access to an interface other than the one from which you entered the adaptive security appliance 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, and entering the management-access command. For more information about the management-access command, see the Cisco ASA 5500 Series Command Reference.


Detailed Steps

To configure management access, perform the following steps:


Step 1 Choose Configuration > Device Management > Management Access > ASDM/HTTPS/Telnet/SSH, then click Add.

The Add Device Access Configuration dialog box appears in the right-hand pane.

Step 2 Choose the type of session from the three options listed: ASDM/HTTPS, Telnet, or SSH.

Step 3 From the Interface Name drop-down list, choose the interface to use for administrative access.

Step 4 In the IP Address field, add the IP address of the network or host that is allowed access. The field allows IPv6 addresses.


Note When you enter a colon (:) in the IP Address field for an IPv6 address, the Netmask field changes to Prefix Length.


Step 5 From the Mask drop-down list, choose the mask associated with the network or host that is allowed access.

Step 6 For ASDM/HTTPS sessions, verify that the Enable HTTP Server check box is checked. This is the default setting.

Step 7 Specify the port number. The default port is 443.

Step 8 Adjust the Idle Timeout or Session Timeout if necessary. There is no timeout value by default. This setting is available only in single, routed mode.

Step 9 For Telnet sessions, the default timeout value is 5 minutes. To change this value, type a new one in the Telnet Timeout field.

Step 10 For SSH sessions, the default timeout value is 5 minutes. To change this value, type a new one in the SSH Timeout field.

Step 11 Click Apply.

The changes are saved to the running configuration.


Using an SSH Client

To gain access to the adaptive security appliance console using SSH, at the SSH client, enter the username asa and enter the login password set by the password command (see the "Configuring the Hostname, Domain Name, and Passwords" section).

When starting an SSH session, a dot (.) displays on the adaptive security appliance console before the SSH user authentication prompt appears, as follows:

hostname(config)# .
 
   

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 adaptive security appliance is busy and has not hung.

Configuring CLI Parameters

This section includes the following topics:

Configuring a Login Banner

Customizing a CLI Prompt

Changing the Console Timeout Period

Configuring a Login Banner

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

Restrictions

After a banner is added, Telnet or SSH sessions to adaptive security appliance may close if:

There is not enough system memory available to process the banner message(s).

A TCP write error occurs when attempting 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:

You have logged in to a secure device. If you are not authorized to access this 
device, 
log out immediately or risk possible criminal consequences.
 
   

See RFC 2196 for guidelines about banner messages.

Detailed Steps


Step 1 Choose the Configuration > Device Management > Management Access > Command Line (CLI) > Banner pane, add your banner text to the field for the type of banner you are creating for the CLI:

Session (exec) banner—This banner appears when a user accesses privileged EXEC mode at the CLI.

Login Banner—This banner appears when a user logs in to the CLI.

Message-of-the-day (motd) Banner—This banner appears when a user first connects to the CLI.

ASDM Banner—This banner appears when a user connects to ASDM, following user authentication. The user is given two options for dismissing the banner:

Continue—Dismiss the banner and complete login as usual.

Disconnect— Dismiss the banner and terminate the connection.

Only ASCII characters are allowed, including new line (Enter), which counts as two characters.

Do not use tabs in the banner, because they are not preserved in the CLI version.

There is no length limit for banners other than those for RAM and flash memory.

You can dynamically add the hostname or domain name of the adaptive security appliance by including the strings $(hostname) and $(domain).

If you configure a banner in the system configuration, you can use that banner text within a context by using the $(system) string in the context configuration.

Step 2 Click Apply.


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 adaptive security appliance. In multiple context mode, the prompt also displays the context name. You can display the following items in the CLI prompt.

context

(Multiple mode only) Displays the name of the current context.

domain

Displays the domain name.

hostname

Displays the hostname.

priority

Displays the failover priority as pri (primary) or sec (secondary).

state

Displays the traffic-passing state of the unit. The following values are displayed for the state:

act—Failover is enabled, and the unit is actively passing traffic.

stby— Failover is enabled, and the unit is not passing traffic and is in a standby, failed, or other non-active state.

actNoFailover—Failover is not enabled, and the unit is actively passing traffic.

stbyNoFailover—Failover is not enabled, and the unit is not passing traffic. This might happen when there is an interface failure above the threshold on the standby unit.


Detailed Steps


Step 1 Choose the Configuration > Device Management > Management Access > CLI Prompt pane, do any of the following to customize the prompt:

To add an attribute to the prompt, click the attribute in the Available Prompts list and then click Add. You can add multiple attributes to the prompt. The attribute is moved from the Available Prompts list to the Selected Prompts list.

To remove an attribute from the prompt, click the attribute in the Selected Prompts list and then click Delete. The attribute is moved from the Selected Prompts list to the Available Prompts list.

To change the order in which the attributes appear in the command prompt, click the attribute in the Selected Prompts list and click Move Up or Move Down to change the order.

The prompt is changed and displays in the CLI Prompt Preview field.

Step 2 Click Apply.

The new prompt is saved to the running configuration.


Changing the Console Timeout Period

To change the console timeout period, or the duration of time the management console remains active before automatically shutting down, perform the following steps.

Detailed Steps


Step 1 Choose the Configuration > Device Management > Management Access > Command Line (CLI) > Console Timeout pane, add a new timeout value in minutes.

To specify unlimited, enter 0. The default value is 0.

Step 2 Click Apply.


Configuring File Access

This section includes the following topics.

Configuring the FTP Client Mode

Configuring the Adaptive Security Appliance as a Secure Copy Server

Configuring the Adaptive Security Appliance as a TFTP Client

Adding Mount Points

Configuring the FTP Client Mode

The adaptive security appliance can use FTP to upload or download image files or configuration files to or from an FTP server. In passive FTP, the client initiates both the control connection and the data connection. The server, which is the recipient of the data connection in passive mode, responds with the port number to which it is listening for the specific connection.

To configure the FTP client to be in passive mode, perform the following steps:


Step 1 From the Configuration > Device Management > Management Access > File Access > FTP Client pane, check Specify FTP mode as passive.

Step 2 Click Apply.

The FTP client configuration is changed and the change is saved to the running configuration.


Configuring the Adaptive Security Appliance as a Secure Copy Server   

You can enable the secure copy server on the adaptive security appliance. Only clients that are allowed to access the adaptive security appliance using SSH can establish a secure copy connection.

This implementation of the secure copy server has the following limitations:

The server can accept and terminate connections for secure copy, but cannot initiate them.

The server does not have directory support. The lack of directory support limits remote client access to the adaptive security appliance internal files.

The server does not support banners.

The server does not support wildcards.

The adaptive security appliance license must have the VPN-3DES-AES feature to support SSH version 2 connections.

To configure the adaptive security appliance as a Secure Copy (SCP) server, perform the following steps:


Step 1 From the Configuration > Device Management > Management Access > File Access > Secure Copy (SCP) Server pane, check Enable secure copy server.

Step 2 Click Apply.

The changes are saved to the running configuration. The adaptive security appliance can function as an SCP server for transferring files from/to the device.


Configuring the Adaptive Security Appliance as a TFTP Client

TFTP is a simple client/server file transfer protocol described in RFC783 and RFC1350 Rev. 2. You can configure the adaptive security appliance as a TFTP client so that it can transfer a copy of its running configuration file to a TFTP server using File > Save Running Configuration to TFTP Client or Tools > Command Line Interface. In this way, you can back up and propagate configuration files to multiple adaptive security appliances.

The adaptive security appliance supports only one TFTP client. The full path to the TFTP client is specified in Configuration > Device Management > Management Access > File Access > TFTP Client. Once configured here, you can use a colon (:) to specify the IP address in the CLI configure net and copy commands. However, any other authentication or configuration of intermediate devices necessary for communication from the adaptive security appliance to the TFTP client is done apart from this function.

To configure the adaptive security appliance as a TFTP client for saving configuration files to a TFTP server, perform the following steps:


Step 1 From the Configuration > Device Management > Management Access > File Access > TFTP Client pane, check Enable.

Step 2 From the Interface Name drop-down list, choose the interface to use as a TFTP client.

Step 3 In the IP Address field, add the IP address of the TFTP server where configuration files will be saved.

Step 4 In the Path field, add the path to the TFTP server where configuration files will be saved.

For example: /tftpboot/asa/config3

Step 5 Click Apply.

The changes are saved to the running configuration. This TFTP server will be used to save the adaptive security appliance configuration files.


Adding Mount Points   

Common Internet File System (CIFS) and File Transfer Protocol (FTP) mount points

This section includes the following topics:

Adding a CIFS Mount Point

Adding a CIFS Mount Point

Adding an FTP Mount Point

Adding a CIFS Mount Point

To define a CIFS mount point, perform the following steps:


Step 1 From the Configuration > Device Management > Management Access > File Access > Mount-Points pane, click Add > CIFS Mount Point.

The Add CIFS Mount Point dialog box appears.

Step 2 Check Enable mount point.

This option attaches the CIFS file system on the adaptive security appliance to the UNIX file tree.

Step 3 In the Mount Point Name field, add the name of an existing CIFS location.

Step 4 In the Server Name or IP Address field, add the name or IP address of the server where the mount point is located.

Step 5 In the Share Name field, add the name of the folder on the CIFS server.

Step 6 In the NT Domain Name field, add the name of the NT Domain where the server resides.

Step 7 In the User Name field, add the name of the user authorized for file system mounting on the server.

Step 8 In the Password field, add the password for the user authorized for file system mounting on the server.

Step 9 In the Confirm Password field, add the password again.

Step 10 Click OK.

The Add CIFS Mount Point dialog box closes.

Step 11 Click Apply.

The mount point is added to the adaptive security appliance and the change is saved to the running configuration.


Adding an FTP Mount Point


Note For an FTP mount point, the FTP Server must have a UNIX directory listing style. Microsoft FTP servers have a default of MS-DOS directory listing style.


To define an FTP mount point, perform the following steps:


Step 1 From the Configuration > Device Management > Management Access > File Access > Mount-Points pane, click Add > FTP Mount Point.

The Add FTP Mount Point dialog box appears.

Step 2 Check the Enable check box.

This option attaches the FTP file system on the adaptive security appliance to the UNIX file tree.

Step 3 In the Mount Point Name field, add the name of an existing FTP location.

Step 4 In the Server Name or IP Address field, add the name or IP address of the server where the mount point is located.

Step 5 In the Mode field, click the radio button for the FTP mode (Active or Passive). When you choose Passive mode, the client initiates both the FTP control connection and data connection. The server responds with the number of its listening port for this connection.

Step 6 In the Path to Mount field, add the directory path name to the FTP file server.

Step 7 In the User Name field, add the name of the user authorized for file system mounting on the server.

Step 8 In the Password field, add the password for the user authorized for file system mounting on the server.

Step 9 In the Confirm Password field, add the password again.

Step 10 Click OK.

The dialog box closes.

Step 11 Click Apply.

The mount point is added to the adaptive security appliance and the change is saved to the running configuration.


Configuring ICMP Access

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

By default, the adaptive security appliance does not respond to ICMP echo requests directed to a broadcast address. You can protect the adaptive security appliance from attacks by limiting the addresses of hosts and networks that are allowed to have ICMP access to the adaptive security appliance.

The adaptive security appliance 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.


Note For allowing ICMP traffic through the adaptive security appliance, see Chapter 31 "Configuring Access Rules."


We recommend 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 adaptive security appliance uses a first match to the ICMP traffic followed by an implicit deny all. 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 adaptive security appliance 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.

To configure ICMP access rules, perform the following steps.

Detailed Steps


Step 1 Choose the Configuration > Device Management > Management Access > ICMP pane, click Add.

Step 2 Choose which version of IP to filter by clicking the appropriate radio button:

Both (filters IPv4 and IPv6 traffic)

IPv4 only

IPv6 only

Step 3 If you want to insert a rule into the ICMP table, click the rule that the new rule will precede, and click Insert.

The Create ICMP Rule dialog box appears in the right-hand pane.

Step 4 From the ICMP Type drop-down list, choose the type of ICMP message for this rule.

Step 5 From the Interface list, choose the destination adaptive security appliance interface the rule is to be applied to.

Step 6 In the IP Address field, do one of the following:

Add a specific IP address for the host or network.

Click Any Address and go to Step 9.

Step 7 From the Mask drop-down list, choose the network mask.

Step 8 Click OK.

The dialog box closes.

Step 9 (Optional) To set ICMP unreachable message limits, set the following options. Increasing the rate limit, along with enabling the "Decrement time to live for a connection" option on the Configuration > Firewall > Service Policy Rules > Rule Actions > Connection Settings dialog box, is required to allow a traceroute through the adaptive security appliance that shows the adaptive security appliance as one of the hops.

Rate Limit—Sets the rate limit of unreachable messages, between 1 and 100 messages per second. The default is 1 message per second.

Burst Size—Sets the burst rate, between 1 and 10. This keyword is not currently used by the system, so you can choose any value.

Step 10 Click Apply.


Configuring Management Access Over a VPN Tunnel

If your VPN tunnel terminates on one interface, but you want to manage the adaptive security appliance by accessing a different interface, you can identify that interface as a management-access interface. For example, if you enter the adaptive security appliance from the outside interface, this feature lets you connect to the inside interface using ASDM, SSH, Telnet, or SNMP; or you can ping the inside interface when entering from the outside interface. Management access is available via the following VPN tunnel types: IPsec clients, IPsec LAN-to-LAN, and the AnyConnect SSL VPN client.

Restrictions

You can define only one management-access interface.

Detailed Steps


Step 1 From the Configuration > Device Management > Management Access > Management Interface pane, choose the interface with the highest security (the inside interface) from the Management Access Interface drop-down list.

Step 2 Click Apply.

The management interface is assigned and the change is saved to the running configuration.


Configuring AAA for System Administrators

This section describes how to enable authentication and command authorization for system administrators. Before you configure AAA for system administrators, first configure the local database or AAA server according to Chapter 32 "Configuring AAA Servers and the Local Database."

This section includes the following topics:

Configuring Authentication for CLI, ASDM, and enable command Access

Limiting User CLI and ASDM Access with Management Authorization

Configuring Command Authorization

Configuring Management Access Accounting

Viewing the Current Logged-In User

Recovering from a Lockout

Configuring Authentication for CLI, ASDM, and enable command Access

If you enable CLI authentication, the adaptive security appliance prompts you for your username and password to log in. After you enter your information, you have access to user EXEC mode.

To enter privileged EXEC mode, enter the enable command or the login command (if you are using the local database only).

If you configure enable authentication, the adaptive security appliance prompts you for your username and password. 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.

For authentication using the local database, you can use the login command, which maintains the username but requires no configuration to turn on authentication.


Note Before the adaptive security appliance can authenticate a Telnet, SSH, or HTTP user, you must first configure access to the adaptive security appliance. See the "Configuring Device Access for ASDM, Telnet, or SSH" section. This configuration identifies the IP addresses that are allowed to communicate with the adaptive security appliance.


Detailed Steps

To configure CLI, ASDM, or enable authentication, perform the following steps:


Step 1 To authenticate users who use the enable command, go to Configuration > Device Management > Users/AAA > AAA Access > Authentication, and configure the following settings:

a. Check the Enable check box.

b. From the Server Group drop-down list, choose a server group name or the LOCAL database.

c. (Optional) If you chose a AAA server, you can configure the adaptive security appliance to use the local database as a fallback method if the AAA server is unavailable. Click the Use LOCAL when server group fails check box. We recommend that you use the same username and password in the local database as the AAA server because the adaptive security appliance prompt does not give any indication which method is being used.

Step 2 To authenticate users who access the CLI or ASDM, go to Configuration > Device Management > Users/AAA > AAA Access > Authentication, and configure the following settings:

a. Check one or more of the following check boxes:

HTTP/ASDM—Authenticates the ASDM client that accesses the adaptive security appliance using HTTPS. You only need to configure HTTP authentication if you want to use a AAA server. By default, ASDM uses the local database for authentication even if you do not configure this command.

Serial—Authenticates users who access the adaptive security appliance using the console port.

SSH—Authenticates users who access the adaptive security appliance using SSH.

Telnet—Authenticates users who access the adaptive security appliance using Telnet.

b. For each service that you checked, from the Server Group drop-down list, choose a server group name or the LOCAL database.

c. (Optional) If you chose a AAA server, you can configure the adaptive security appliance to use the local database as a fallback method if the AAA server is unavailable. Click the Use LOCAL when server group fails check box. We recommend that you use the same username and password in the local database as the AAA server because the adaptive security appliance prompt does not give any indication which method is being used.

Step 3 Click Apply.


Detailed Steps

Limiting User CLI and ASDM Access with Management Authorization

If you configure CLI or enable authentication, you can limit a local user, RADIUS, TACACS+, or LDAP user (if you map LDAP attributes to RADIUS attributes) from accessing the CLI, ASDM, or the enable command.


Note Serial access is not included in management authorization, so if you enable the Authentication > Serial option, then any user who authenticates can access the console port.


Detailed Steps

To configure management authorization, perform the following steps:


Step 1 To enable management authorization, go to Configuration > Device Management > Users/AAA > AAA Access > Authorization, and check the Perform authorization for exec shell access > Enable check box.

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 the "Configuring Local Command Authorization" section for more information.

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—Configure the Service-Type attribute for one of the following values.

RADIUS or LDAP (mapped) users—Use the IETF RADIUS numeric Service-Type attribute which maps to one of the following values.

Service-Type 6 (Administrative)—Allows full access to any services specified by the Authentication tab options

Service-Type 7 (NAS prompt)—Allows access to the CLI when you configure the Telnet or SSH authentication options, but denies ASDM configuration access if you configure the HTTP option. ASDM monitoring access is allowed. If you configure enable authentication with the Enable option, the user cannot access privileged EXEC mode using the enable command.

Service-Type 5 (Outbound)—Denies management access. The user cannot use any services specified by the Authentication tab options (excluding the Serial option; serial access is allowed). Remote-access (IPSec and SSL) users can still authenticate and terminate their remote-access sessions.

TACACS+ users—Authorization is requested with the "service=shell" and the server responds with PASS or FAIL.

PASS, privilege level 1—Allows full access to any services specified by the Authentication tab options.

PASS, privilege level 2 and higher—Allows access to the CLI when you configure the Telnet or SSH authentication options, but denies ASDM configuration access if you configure the HTTP option. ASDM monitoring access is allowed. If you configure enable authentication with the Enable option, the user cannot access privileged EXEC mode using the enable command.

FAIL—Denies management access. The user cannot use any services specified by the Authentication tab options (excluding the Serial option; serial access is allowed).

Local users—Configure the Access Restriction option. See the "Adding a User Account" section. By default, the access restriction is Full Access, which allows full access to any services specified by the Authentication tab options.


Configuring Command Authorization

If you want to control the access to commands, the adaptive security appliance 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.

This section includes the following topics:

Command Authorization Overview

Configuring Local Command Authorization

Configuring TACACS+ Command Authorization

Command Authorization Overview

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 adaptive security appliance. When a local, RADIUS, or LDAP (if you map LDAP attributes to RADIUS attributes) user authenticates for CLI access, the adaptive security appliance 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 user's 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 adaptive security appliance 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 adaptive security appliance places you in level n. These levels are not used unless you turn on local command authorization (see "Configuring Local Command Authorization"). (See the Cisco ASA 5500 Series 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 they authenticate for CLI access. Every command that a user enters at the CLI is checked with the TACACS+ server.

About Preserving User Credentials

When a user logs into the adaptive security appliance, they are required to provide a username and password for authentication. The adaptive security appliance 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 upon 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.

Local server is configured to authenticate user access.

Privilege level 15 command access is configured to require a password.

User's account is configured for serial only authorization (no access to console or ASDM).

User's account is configured for privilege level 15 command access.

The following table shows how credentials are used in this case by the adaptive security appliance.

Credentials required
Username and Password Authentication
Serial
Authorization
Privileged Mode Command Authorization
Privileged
Mode Exit Authorization

Username

Yes

No

No

Yes

Password

Yes

No

No

Yes

Privileged Mode Password

No

No

Yes

No


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 between contexts.

When configuring command authorization, you must configure each security context separately. This 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 what 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 they need.


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


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 their privilege level or below. The adaptive security appliance 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 "Configuring LDAP Attribute Maps" section.)

This section includes the following topics:

Local Command Authorization Prerequisites

Default Command Privilege Levels

Assigning Privilege Levels to Commands and Enabling Authorization

Viewing Command Privilege Levels

Local Command Authorization Prerequisites

Complete the following tasks as part of your command authorization configuration:

Configure enable authentication. (See the "Configuring Authentication for CLI, ASDM, and enable command Access" section.)

enable authentication is essential to maintain 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.

To configure the local database, see the "Adding a User Account" section.

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 VAS CVPN3000-Privilege-Level according to the "Configuring LDAP Attribute Maps" section.

Default Command Privilege Levels

By default, the following commands are assigned to privilege level 0. All other commands are at 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 the "Viewing Command Privilege Levels" section.

Assigning Privilege Levels to Commands and Enabling Authorization

This section assigns a command to a new privilege level, and enables authorization.

Detailed Steps


Step 1 To enable command authorization, go to Configuration > Device Management > Users/AAA > AAA Access > Authorization, and check Enable authorization for command access > Enable.

Step 2 From the Server Group drop-down list, choose LOCAL.

Step 3 When you enable local command authorization, you have the option of manually assigning privilege levels to individual commands or groups of commands or enabling the predefined user account privileges.

To use predefined user account privileges, click Set ASDM Defined User Roles.

The ASDM Defined User Roles Setup dialog box shows the commands and their levels. Click Yes to use the predefined user account privileges: Admin (privilege level 15, with full access to all CLI commands; Read Only (privilege level 5, with read-only access); and Monitor Only (privilege level 3, with access to the Monitoring section only).

To manually configure command levels, click Configure Command Privileges.

The Command Privileges Setup dialog box appears. You can view all commands by choosing --All Modes-- from the Command Mode drop-down list, or you can choose a configuration mode to view the commands available in that mode. For example, if you choose context, you can view all commands available in context configuration mode. If a command can be entered in user EXEC/privileged EXEC mode as well as configuration mode, and the command performs different actions in each mode, you can set the privilege level for these modes separately.

The Variant column displays show, clear, or cmd. You can set the privilege only for the show, clear, or configure form of the command. The configure form of the command is typically the form that causes a configuration change, either as the unmodified command (without the show or clear prefix) or as the no form.

To change the level of a command, double-click it or click Edit. You can set the level between 0 and 15. You can only configure the privilege level of the main command. For example, you can configure the level of all aaa commands, but not the level of the aaa authentication command and the aaa authorization command separately.

To change the level of all shown commands, click Select All and then Edit.

Click OK to accept your changes.

Step 4 To support administrative user privilege levels from RADIUS, check Perform authorization for exec shell access > Enable.

Without this option, the adaptive security appliance only supports privilege levels for local database users and defaults all other types of users to level 15.

This option also enables management authorization for local, RADIUS, LDAP (mapped), and TACACS+ users. See the "Limiting User CLI and ASDM Access with Management Authorization" section for more information.

Step 5 Click Apply.


Viewing Command Privilege Levels

The following commands when used in Tools > Command Line Interface let you view privilege levels for commands.

Command
Purpose

show running-config all privilege all

Shows all commands.

show running-config privilege level level

Shows commands for a specific level. The level is an integer between 0 and 15.

show running-config privilege command command

Shows the level of a specific command.


Examples

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

Enter the following command in the Tools > Command Line Interface tool:

show running-config all privilege all
privilege show level 15 command aaa
privilege clear level 15 command aaa
privilege configure level 15 command aaa
privilege show level 15 command aaa-server
privilege clear level 15 command aaa-server
privilege configure level 15 command aaa-server
privilege show level 15 command access-group
privilege clear level 15 command access-group
privilege configure level 15 command access-group
privilege show level 15 command access-list
privilege clear level 15 command access-list
privilege configure level 15 command access-list
privilege show level 15 command activation-key
privilege configure level 15 command activation-key
....
 
   

The following command displays the command assignments for privilege level 10:

show running-config privilege level 10
privilege show level 10 command aaa
 
   

The following command displays the command assignment for the access-list command:

show running-config privilege command access-list
privilege show level 15 command access-list
privilege clear level 15 command access-list
privilege configure level 15 command access-list

Configuring TACACS+ Command Authorization

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

When configuring command authorization with a TACACS+ server, do not save your configuration until you are sure it works the way you want. If you get locked out because of a mistake, you can usually recover access by restarting the adaptive security appliance. If you still get locked out, see the "Recovering from a Lockout" section.

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 adaptive security appliance. 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 the "Configuring Command Authorization" section.

This section includes the following topics:

TACACS+ Command Authorization Prerequisites

Configuring Commands on the TACACS+ Server

Enabling TACACS+ Command Authorization

TACACS+ Command Authorization Prerequisites

Complete the following tasks as part of your command authorization configuration:

Configure CLI and enable authentication (see the "Configuring Local Command Authorization" section).

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 adaptive security appliance 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 adaptive security appliance 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, and 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 ?, which shows CLI usage (see Figure 33-1).

Figure 33-1 Permitting All Related Commands

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 (see Figure 33-2).

Figure 33-2 Permitting Single Word Commands

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 (see Figure 33-3).

Figure 33-3 Disallowing Arguments

When you abbreviate a command at the command line, the adaptive security appliance 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 adaptive security appliance sends the entire command to the TACACS+ server, show logging. However, if you enter sh log mess, then the adaptive security appliance 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 (see Figure 33-4).

Figure 33-4 Specifying 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

Enabling TACACS+ Command Authorization

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

Detailed Steps


Step 1 To perform command authorization using a TACACS+ server, go to Configuration > Device Management > Users/AAA > AAA Access > Authorization, and check the Enable authorization for command access > Enable check box.

Step 2 From the Server Group drop-down list, choose a AAA server group name.

Step 3 (Optional) you can configure the adaptive security appliance to use the local database as a fallback method if the AAA server is unavailable. Click the Use LOCAL when server group fails check box. We recommend that you use the same username and password in the local database as the AAA server because the adaptive security appliance prompt does not give any indication which method is being used. Be sure to configure users in the local database (see the "Adding a User Account" section) and command privilege levels (see the "Configuring Local Command Authorization" section).

Step 4 Click Apply.


Configuring Management Access Accounting

You can configure accounting when users log in, when they enter the enable command, or when they issue commands.

Prerequisites

You can only account for users that first authenticate with the adaptive security appliance, so configure authentication using the "Configuring Authentication for CLI, ASDM, and enable command Access" section.

For information about configuring a AAA server group, see the "Configuring AAA Server Groups" section. For CLI access, you can use TACACS+ or RADIUS servers. For command accounting, you can only use TACACS+ servers.

Detailed Steps


Step 1 To enable accounting of users when they enter the enable command:

a. Go to Configuration > Device Management > Users/AAA > AAA Access > Accounting, and check the Require accounting to allow accounting of user activity > Enable check box.

b. From the Server Group drop-down list, choose a RADIUS or TACACS+ server group name.

Step 2 To enable accounting of users when they access the adaptive security appliance using Telnet, SSH, or the serial console:

a. Under the Require accounting for the following types of connections area, check the check boxes for Serial, SSH, and/or Telnet.

b. For each connection type, from the Server Group drop-down list, choose a RADIUS or TACACS+ server group name.

Step 3 To configure command accounting:

a. Under the Require command accounting area, check Enable.

b. From the Server Group drop-down list, choose a TACACS+ server group name. RADIUS is not supported.

You can send accounting messages to the TACACS+ accounting server when you enter any command other than show commands at the CLI.

c. If you customize the command privilege level using the Command Privilege Setup dialog box (see the "Assigning Privilege Levels to Commands and Enabling Authorization" section), you can limit which commands the adaptive security appliance accounts for by specifying a minimum privilege level in the Privilege level drop-down list. The adaptive security appliance does not account for commands that are below the minimum privilege level.

Step 4 Click Apply.


Viewing the Current Logged-In User

To view the current logged-in user, enter the following command in Tools > Command Line Interface:

show curpriv
 
   

See the following sample show curpriv command output. A description of each field follows.

show curpriv
Username : admin
Current privilege level : 15
Current Mode/s : P_PRIV
 
   

Table 33-1 describes the show curpriv command output.

Table 33-1 show curpriv Command Output Description

Field
Description

Username

Username. If you are logged in as the default user, the name is enable_1 (user EXEC) or enable_15 (privileged EXEC).

Current privilege level

Level from 0 to 15. Unless you configure local command authorization and assign commands to intermediate privilege levels, levels 0 and 15 are the only levels that are used.

Current Mode/s

Shows the access modes:

P_UNPR—User EXEC mode (levels 0 and 1)

P_PRIV—Privileged EXEC mode (levels 2 to 15)

P_CONF—Configuration mode


Recovering from a Lockout

In some circumstances, when you turn on command authorization or CLI authentication, you can be locked out of the adaptive security appliance CLI. You can usually recover access by restarting the adaptive security appliance. However, if you already saved your configuration, you might be locked out. Table 33-2 lists the common lockout conditions and how you might recover from them.

Table 33-2 CLI Authentication and Command Authorization Lockout Scenarios 

Feature
Lockout Condition
Description
Workaround: Single Mode
Workaround: Multiple Mode

Local CLI authentication

No users in the local database

If you have no users in the local database, you cannot log in, and you cannot add any users.

Log in and reset the passwords and aaa commands.

Session into the adaptive security appliance from the switch. From the system execution space, you can change to the context and add a user.

TACACS+ command authorization

TACACS+ CLI authentication

RADIUS CLI authentication

Server down or unreachable and you do not have the fallback method configured

If the server is unreachable, then you cannot log in or enter any commands.

1. Log in and reset the passwords and AAA commands.

2. Configure the local database as a fallback method so you do not get locked out when the server is down.

1. If the server is unreachable because the network configuration is incorrect on the adaptive security appliance, session into the adaptive security appliance from the switch. From the system execution space, you can change to the context and reconfigure your network settings.

2. Configure the local database as a fallback method so you do not get locked out when the server is down.

TACACS+ command authorization

You are logged in as a user without enough privileges or as a user that does not exist

You enable command authorization, but then find that the user cannot enter any more commands.

Fix the TACACS+ server user account.

If you do not have access to the TACACS+ server and you need to configure the adaptive security appliance immediately, then log into the maintenance partition and reset the passwords and aaa commands.

Session into the adaptive security appliance from the switch. From the system execution space, you can change to the context and complete the configuration changes. You can also disable command authorization until you fix the TACACS+ configuration.

Local command authorization

You are logged in as a user without enough privileges

You enable command authorization, but then find that the user cannot enter any more commands.

Log in and reset the passwords and aaa commands.

Session into the adaptive security appliance from the switch. From the system execution space, you can change to the context and change the user level.