Cisco Security Appliance Configuration Guide using ASDM, 6.2
Managing Device Access
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Configuring Management Access

Table Of Contents

Configuring Management Access

Configuring Device Access for ASDM, Telnet, or SSH   

Configuring CLI Parameters

Adding a Banner

Customizing a CLI Prompt

Changing the Console Timeout Period

Configuring File Access

Configuring the FTP Client Mode

Configuring the Security Appliance as a Secure Copy Server   

Configuring the Security Appliance as a TFTP Client

Adding Mount Points   

Adding a CIFS Mount Point

Adding an FTP Mount Point

ICMP Access

Configuring a Management Interface

Configuring SNMP

Information About SNMP

Information About SNMP Terminology

Information About the Management Information Base and Traps

Configuring SNMP Parameters and Management Stations 

Configuring SNMP Parameters for Versions 1 and 2c

Configuring SNMP Parameters for Version 3

Adding an SNMP Management Station

Configuring SNMP Traps

Configuring Management Access Rules    

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

About Preserving User Credentials

Configuring Local Command Authorization

Configuring TACACS+ Command Authorization

Configuring Management Access Accounting

Recovering from a Lockout


Configuring Management Access


This chapter contains the following topics:

Configuring Device Access for ASDM, Telnet, or SSH

Configuring CLI Parameters

Configuring File Access

ICMP Access

Configuring a Management Interface

Configuring SNMP

Configuring Management Access Rules

Configuring AAA for System Administrators


Note To configure the Management IP address for transparent firewall mode, see the "Configuring the Management IP Address for Transparent Firewall Mode" section on page 8-1.


Configuring Device Access for ASDM, Telnet, or SSH   

This section describes how to allow clients to access the device using ASDM, Telnet, or SSH. To configure access to the security appliance, perform the following steps:


Step 1 From the Configuration > Device Management > Management Access > ASDM/HTTPS/Telnet/SSH pane, 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.


Configuring CLI Parameters

This section includes the following topics:

Adding a Banner

Customizing a CLI Prompt

Changing the Console Timeout Period

Adding a Banner

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

See the following 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.

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 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

After a banner is added, security appliance Telnet or SSH sessions 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).

To add a message of the day, login, or session banner, perform the following steps:


Step 1 From 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.

Step 2 Click Apply.

The banner is added and the changes are saved to the running configuration.


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 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.


To customize the prompt used during CLI sessions so that it shows something other than the hostname or context name, complete the following steps:


Step 1 From 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:


Step 1 From 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.

The console timeout is changed, and the changes are saved to the running configuration.


Configuring File Access

This section includes the following topics.

Configuring the FTP Client Mode

Configuring the Security Appliance as a Secure Copy Server

Configuring the Security Appliance as a TFTP Client

Adding Mount Points

Configuring the FTP Client Mode

The 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 Security Appliance as a Secure Copy Server   

You can enable the secure copy server on the security appliance. Only clients that are allowed to access the 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 security appliance internal files.

The server does not support banners.

The server does not support wildcards.

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

To configure the 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 security appliance can function as an SCP server for transferring files from/to the device.


Configuring the 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 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 security appliances.

The 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 security appliance to the TFTP client is done apart from this function.

To configure the 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 security appliance configuration files. For more information, see Save the Running Configuration to a TFTP Server, page 5-4.


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 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 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 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 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 security appliance and the change is saved to the running configuration.


ICMP Access

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


Note For allowing ICMP traffic through the security appliance, see the "Configuring Access Rules and ACLs" section on page 21-1.


It is recommended that permission is always granted 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 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 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:


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

Step 2 Choose which version of the Internet Protocol 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.

Table 18-1 lists the types of ICMP messages.

Table 18-1 ICMP Type Literals 

ICMP Type
Literal

0

echo-reply

3

unreachable

4

source-quench

5

redirect

6

alternate-address

8

echo

9

router-advertisement

10

router-solicitation

11

time-exceeded

12

parameter-problem

13

timestamp-request

14

timestamp-reply

15

information-request

16

information-reply

17

mask-request

18

mask-reply

31

conversion-error

32

mobile-redirect


Step 5 From the Interface selection list, choose the destination 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 security appliance that shows the 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.

The ICMP rule is added to the end of the ICMP table, and the change is saved to the running configuration.


Configuring a Management Interface

A high-security interface can be identified to manage the security appliance. When a management interface is assigned, ASDM can run on it with a fixed IP address over an IPSec VPN tunnel. This is possible if VPN is configured on the security appliance and the external interface is using a dynamically assigned IP address. The management interface is also used when accessing and managing the security appliance securely from home using the VPN client.


Note If your security appliace is configured for failover, we recommend that you configure at least one management interface with the standby IP address.


To configure a management interface, perform the following 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 SNMP

This section describes how to configure SNMP, and includes the following topics:

Information About SNMP

Configuring SNMP Parameters and Management Stations

Configuring SNMP Traps

Information About SNMP

The Simple Network Management Protocol (SNMP) enables the monitoring of network devices from a central location. The security appliance supports network monitoring using SNMP Versions 1, 2c, and 3, as well as traps and SNMP read access, but does not support SNMP write access.

You can configure the security appliance to send traps (event notifications) to a network management station (NMS), or you can use the NMS to browse the MIBs on the security appliance. Use CiscoWorks for Windows or any other SNMP MIB-II-compliant browser to receive SNMP traps and browse a MIB.

The security appliance has an SNMP agent that notifies designated management stations if events occur that are pre-defined to require a notification, for example, when a link in the network goes up or down. The notification it sends includes an SNMP OID, identifying itself to the management stations.

The security appliance SNMP agent also replies when a management station asks for information.

This section includes the following topics:

Information About SNMP Terminology

Information About the Management Information Base and Traps

Information About SNMP Terminology

The following terms are commonly used when working with SNMP:

Term
Description

Agent

The SNMP server running on the security appliance. The agent responds to requests for information and actions from the management station. The agent also controls access to the its management information base (MIB), the collection of objects that can be viewed or changed by the SNMP manager.

Browsing

Monitoring the health of a device from the management station by polling required information from the device SNMP agent. This activity may include issuing a series of GET-NEXT or GET-BULK requests of the MIB tree from the management station to determine values.

Management stations

The PCs or workstations set up to monitor SNMP events and manage devices such as the security appliance.

MIB

Management Information Bases, or standardized data structures, for collecting information about packets, connections, buffers, failovers, and so on. MIBs are defined by product and the protocols and hardware standards used by most network devices. SNMP management stations can browse MIBs and request specific data or events be sent as they occur. Some MIB data can be modified for administrative purposes.

OID

The system object identifier (OID) that identifies a device to its management station and indicates to users the source of information monitored and displayed.

Trap

Predefined events that generate a message from the SNMP agent to the management station. Events include alarm conditions such as linkup, linkdown, coldstart, authentication, or syslog events.


Information About the Management Information Base and Traps

MIBs are either standard or enterprise-specific. Standard MIBs are created by the IETF and documented in various RFCs. A trap reports significant events occurring on a network device, most often errors or failures. SNMP traps are defined in either standard or enterprise-specific MIBs. Standard traps are created by the IETF and documented in various RFCs. Standard traps are compiled into the security appliance software.

If needed, you can also download RFCs, standard MIBS, and standard traps from the IETF website:

http://www.ietf.org/

Download Cisco MIBs and OIDs from the following location:

http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml

Download Cisco OIDs from the following location:

ftp://ftp.cisco.com/pub/mibs/oid/oid.tar.gz

Configuring SNMP Parameters and Management Stations 

This section includes the following topics:

Configuring SNMP Parameters for Versions 1 and 2c

Configuring SNMP Parameters for Version 3

Adding an SNMP Management Station

Configuring SNMP Parameters for Versions 1 and 2c

To configure SNMP parameters for Versions 1 and 2c, perform the following steps:


Step 1 In the ASDM main window, choose Configuration > Device Management > Management Access > SNMP.

Step 2 In the Community String (default) field, enter a default community string, which applies to SNMP Versions 1 and 2c only. To configure SNMP parameters for Version 3, see Configuring SNMP Parameters for Version 3.

Enter the password used by the SNMP management stations when sending requests to the security appliance. The SNMP community string is a shared secret among the SNMP management stations and the network nodes being managed. The security appliance uses the password to determine if the incoming SNMP request is valid. The password is a case-sensitive value up to 32 characters in length. Spaces are not permitted. The default is "public." SNMP Version 2c allows separate community strings to be set for each management station. If no community string is configured for any management station, the value set here will be used by default.

Step 3 In the Contact field, enter the name of the security appliance system administrator. The text is case-sensitive and can be up to 127 characters. Spaces are accepted, but multiple spaces are shortened to a single space.

Step 4 In the Location field, enter the location of the security appliance being managed by SNMP. The text is case-sensitive and can be up to 127 characters. Spaces are accepted, but multiple spaces are shortened to a single space.

Step 5 In the Listening Port field, enter the number of the security appliance port that listens for SNMP requests from management stations; or keep the default, port number161.

Step 6 Click Apply.

SNMP parameters for Versions 1 and 2c are configured and the changes are saved to the running configuration.


Configuring SNMP Parameters for Version 3

SNMP Version 3 allows you to configure additional authentication and privacy options for more secure protocol operations by means of SNMP server groups and users. To configure SNMP parameters for Version 3, perform the following steps:


Step 1 In the ASDM main window, choose Configuration > Device Management > Management Access > SNMP.

Step 2 In the SNMPv3 Users pane, to add a configured user or a new user to a group, click Add. To change user parameters, click Edit. To remove a configured user from a group, click Delete. When you remove the last user in a group, ASDM deletes the group.


Note Once a user is created, you cannot change the group to which the user belongs.


The Add SNMP User Entry dialog box appears.

Step 3 In the Group Name drop-down list, choose the group to which the SNMP user will belong. The available groups are as follows:

Auth&Encryption, in which users have authentication and encryption configured

Authentication_Only, in which users have only authentication configured

No_Authentication, in which users have neither authentication nor encryption configured

Step 4 In the Username field, enter the name of a configured user or a new user. The username must be unique for the SNMP server group selected.

Step 5 To have the password encrypted, click the Encrypt Password radio button. If you choose this option, you must enter the password as an MD5 hash value.

Step 6 Indicate the type of authentication you want to use by clicking one of the two radio buttons: MD5 or SHA.

Step 7 In the Authentication Password field, type the password to use for authentication.

Step 8 Indicate the type of encryption you want to use by clicking one of these three radio buttons: DES, 3DES, or AES.

Step 9 If you chose AES encryption, then from the AES Size drop-down list, specify which level of AES encryption to use: 128, 192, or 256.

Step 10 In the Encryption Password field, type the password to use for encryption. The maximum number of characters allowed for this password is 64.

Step 11 Click OK to create a group (if this is the first user in that group), display this group in the Group Name drop-down list, and create a user for that group.

The Add SNMP User Entry dialog box closes.

The SNMPv3 Users pane lists the following information: SNMP Version 3 server group name, name of the user that belongs to the specified group, encrypted password setting, authentication setting, encryption algorithm setting, and the AES size setting.

Step 12 Click Apply.

SNMP parameters for Version 3 are configured, and the changes are saved to the running configuration.


Adding an SNMP Management Station

To add an SNMP management station, perform the following steps:


Step 1 In the ASDM main window, choose Configuration > Device Management > Management Access > SNMP.

Step 2 In the SNMP Management Stations pane, click Add.

The Add SNMP Host Access Entry dialog box appears.

Step 3 In the Interface Name drop-down list, choose the interface on which the SNMP host resides.

Step 4 In the IP Address field, enter the SNMP host IP address.

Step 5 In the UDP Port field, enter the SNMP host UDP port, or keep the default, port 162.

Step 6 In the Community String field, add the SNMP host community string. If no community string is specified for a management station, the value set in the Community String (default) field on the SNMP Management Stations pane is used.

Step 7 In the SNMP Version drop-down list, choose the SNMP version used by the SNMP host.

Step 8 If you have selected SNMP Version 3 in the previous step, in the Username drop-down list, choose the name of a configured user.

Step 9 To specify the method for communicating with this management station, check the Poll or Trap check boxes.

Step 10 Click OK.

The Add SNMP Host Access Entry dialog box closes.

Step 11 Click Apply.

The management station is configured and changes are saved to the running configuration.


Configuring SNMP Traps

To designate which traps the SNMP agent generates and how they are collected and sent to network management stations, perform the following steps:


Step 1 In the ASDM main window, choose Configuration > Device Management > Management Access > SNMP.

Step 2 Click Configure Traps.

The SNMP Trap Configuration dialog box appears.

Step 3 Check the applicable check boxes for the SNMP events to notify through SNMP traps.

Step 4 Click OK.

The SNMP Trap Configuration dialog box closes.

Step 5 Click Apply.

The SNMP traps are configured and the changes are saved to the running configuration.


Configuring Management Access Rules    

Access Rules specifically permit or deny traffic to or from a particular peer (or peers), while Management Access Rules provide access control for to-the-box traffic. For example, in addition to detecting IKE Denial of Service attacks, you can block them using management access rules.

To add a Management Access Rule, perform the following steps:


Step 1 Choose Configuration > Device Management > Management Access > Management Access Rules.

Step 2 Click Add, and choose one of the following actions:

Add Management Access Rule

Add IPv6 Management Access Rule

The appropriate Add Management Access Rule dialog box appears.

Step 3 From the Interface drop-down list, choose an interface on which to apply the rule.

Step 4 In the Action field, click one of the following:

Permit (permits this traffic)

Deny (denies this traffic)

Step 5 In the Source field, choose Any, or click the ellipsis (...) to browse for an address.

Step 6 In the Service field, add a service name for rule traffic, or click the ellipsis (...) to browse for a service.

Step 7 (Optional) In the Description field, add a description for this management access rule.

Step 8 (Optional) If you want to receive log messages for this access rule, check Enable Logging, and then from the Logging Level drop-down list, choose the log level to apply. The default level is Informational.

Step 9 (Optional) To configure advanced options, click More Options to configure the following settings:

If you want to turn off this Management Access Rule, uncheck Enable Rule.

Add a source service in the Source Service field, or click the ellipsis (...) to browse for a service.

The destination service and source service must be the same. Copy and paste the destination Service field to the Source Service field.

To configure the logging interval (if you enable logging and choose a non-default setting), enter a value in seconds in the Logging Interval field.

To select a predefined time range for this rule, from the Time Range drop-down list, choose a time range; or click the ellipsis (...) to browse for a time range.

The Add Time Range dialog box appears. For information about adding a time range, see Configuring Time Ranges, page 20-15.

Step 10 Click OK. The dialog box closes and the Management Access rule is added.

Step 11 Click Apply. The rule is saved in the running configuration.


Note After you create management access rules, you can click the radio buttons at the bottom of the pane to sort the display and show both IPv4 and IPv6 rules, IPv4 only, or IPv6 only.



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 the "AAA Server and Local Database Support" section on page 16-3 or the "Configuring AAA Server Groups" section on page 16-9.

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

Recovering from a Lockout

Configuring Authentication for CLI, ASDM, and enable command Access

If you enable CLI authentication, the 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 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 security appliance can authenticate a Telnet, SSH, or HTTP user, you must first configure access to the security appliance according to the "Configuring Device Access for ASDM, Telnet, or SSH" section. These panes identify the IP addresses that are allowed to communicate with the security appliance.


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 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 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 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 security appliance using the console port.

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

Telnet—Authenticates users who access the 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 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 security appliance prompt does not give any indication which method is being used.

Step 3 Click Apply.


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.


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 on page 16-18. 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 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 security appliance. When a local, RADIUS, or LDAP (if you map LDAP attributes to RADIUS attributes) user authenticates for CLI access, the 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 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 security appliance places you in level n. These levels are not used unless you turn on local command authorization (see "Configuring Local Command Authorization" below). (See the Cisco ASA 5500 Series Command Reference for more information about enable.)


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 security appliance, they are required to provide a username and password for authentication. The 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 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 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 on page 16-22.)

This section includes the following topics:

Local Command Authorization Prerequisites

Default Command Privilege Levels

Assigning Privilege Levels to Commands and Enabling Authorization

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 "AAA Server and Local Database Support" section on page 16-3.

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 on page 16-22.

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.

Assigning Privilege Levels to Commands and Enabling Authorization

To assign a command to a new privilege level, and enable authorization, follow these 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 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.


Configuring TACACS+ Command Authorization

If you enable TACACS+ command authorization, and a user enters a command at the CLI, the 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 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 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

Configure CLI and enable authentication (see the "Configuring Authentication for CLI, ASDM, and enable command Access" 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 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 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 box, and type permit aaa-server in the arguments box.

You can permit all arguments of a command that you do not explicitly deny by selecting 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 show CLI usage (see Figure 18-1).

Figure 18-1 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 18-2).

Figure 18-2 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 box, and deny password in the arguments box. Be sure to select the Permit Unmatched Args check box so that enable alone is still allowed (see Figure 18-3).

Figure 18-3 Disallowing Arguments

When you abbreviate a command at the command line, the 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 security appliance sends the entire command to the TACACS+ server, show logging. However, if you enter sh log mess, then the 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 18-4).

Figure 18-4 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 security appliance as a user that is defined on the TACACS+ server, and that you have the necessary command authorization to continue configuring the security appliance. For example, you should log in as an admin user with all commands authorized. Otherwise, you could become unintentionally locked out.

To configure TACACS+ command authorization, perform the following 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 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 security appliance prompt does not give any indication which method is being used.

Step 4 Click Apply.


Configuring Management Access Accounting

To enable accounting for management access, perform the following steps:


Step 1 You can only account for users that first authenticate with the security appliance, so configure authentication using the "Configuring Authentication for CLI, ASDM, and enable command Access" section.

Step 2 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 3 To enable accounting of users when they access the 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 4 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 security appliance accounts for by specifying a minimum privilege level in the Privilege level drop-down list. The security appliance does not account for commands that are below the minimum privilege level.

Step 5 Click Apply.


Recovering from a Lockout

In some circumstances, when you turn on command authorization or CLI authentication, you can be locked out of the security appliance CLI. You can usually recover access by restarting the security appliance. However, if you already saved your configuration, you might be locked out. Table 18-2 lists the common lockout conditions and how you might recover from them.

Table 18-2 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 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 security appliance, session into the 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 security appliance immediately, then log into the maintenance partition and reset the passwords and aaa commands.

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