Table Of Contents

Administering the Switch

Preventing Unauthorized Access to Your Switch

Protecting Access to Privileged EXEC Commands

Default Password and Privilege Level Configuration

Setting or Changing a Static Enable Password

Protecting Enable and Enable Secret Passwords with Encryption

Setting a Telnet Password for a Terminal Line

Configuring Username and Password Pairs

Configuring Multiple Privilege Levels

Setting the Privilege Level for a Command

Changing the Default Privilege Level for Lines

Logging into and Exiting a Privilege Level

Controlling Switch Access with TACACS+

Understanding TACACS+

TACACS+ Operation

Configuring TACACS+

Default TACACS+ Configuration

Identifying the TACACS+ Server Host and Setting the Authentication Key

Configuring Login Authentication

Configuring TACACS+ Authorization for EXEC Access and Network Services

Starting TACACS+ Accounting

Configuring the Switch for Local Authentication and Authorization

Displaying the TACACS+ Configuration

Managing the System Time and Date

Understanding the System Clock

Understanding Network Time Protocol

Configuring NTP

Default NTP Configuration

Configuring NTP Authentication

Configuring NTP Associations

Configuring NTP Broadcast Service

Configuring NTP Access Restrictions

Configuring the Source IP Address for NTP Packets

Displaying the NTP Configuration

Configuring Time and Date Manually

Setting the System Clock

Displaying the Time and Date Configuration

Configuring the Time Zone

Configuring Summer Time (Daylight Saving Time)

Configuring a System Name and Prompt

Default System Name and Prompt Configuration

Configuring a System Name

Configuring a System Prompt

Understanding DNS

Default DNS Configuration

Setting Up DNS

Displaying the DNS Configuration

Creating a Banner

Default Banner Configuration

Configuring a Message-of-the-Day Login Banner

Configuring a Login Banner

Managing the MAC Address Table

Building the Address Table

MAC Addresses and VLANs

Default MAC Address Table Configuration

Changing the Address Aging Time

Removing Dynamic Address Entries

Adding and Removing Static Address Entries

Displaying Address Table Entries

Optimizing System Resources for User-Selected Features

Administering the Switch

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This chapter describes how to perform one-time operations to administer your switch. This chapter consists of these sections:

•Preventing Unauthorized Access to Your Switch

•Protecting Access to Privileged EXEC Commands

•Controlling Switch Access with TACACS+

•Managing the System Time and Date

•Configuring a System Name and Prompt

•Creating a Banner

•Managing the MAC Address Table

•Optimizing System Resources for User-Selected Features

Preventing Unauthorized Access to Your Switch

You can prevent unauthorized users from reconfiguring your switch and viewing configuration information. Typically, you want network administrators to have access to your switch while you restrict access to users who dial from outside the network through an asynchronous port, connect from outside the network through a serial port, or connect through a terminal or workstation from within the local network.

To prevent unauthorized access into your switch, you should configure one or more of these security features:

•At a minimum, you should configure passwords and privileges at each switch port. These passwords are locally stored on the switch. When users attempt to access the switch through a port or line, they must enter the password specified for the port or line before they can access the switch. For more information, see the "Protecting Access to Privileged EXEC Commands" section.

•For an additional layer of security, you can also configure username and password pairs, which are locally stored on the switch. These pairs are assigned to lines or interfaces and authenticate each user before that user can access the switch. If you have defined privilege levels, you can also assign a specific privilege level (with associated rights and privileges) to each username and password pair. For more information, see the "Configuring Username and Password Pairs" section.

•If you want to use username and password pairs, but you want to store them centrally on a server instead of locally, you can store them in a database on a security server. Multiple networking devices can then use the same database to obtain user authentication (and, if necessary, authorization) information. For more information, see the "Controlling Switch Access with TACACS+" section.

Protecting Access to Privileged EXEC Commands

A simple way of providing terminal access control in your network is to use passwords and assign privilege levels. Password protection restricts access to a network or network device. Privilege levels define what commands users can issue after they have logged into a network device.

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Note For complete syntax and usage information for the commands used in this section, refer to the Cisco IOS Security Command Reference for Release 12.1.

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This section describes how to control access to the configuration file and privileged EXEC commands. It contains this configuration information:

•Default Password and Privilege Level Configuration

•Setting or Changing a Static Enable Password

•Protecting Enable and Enable Secret Passwords with Encryption

•Setting a Telnet Password for a Terminal Line

•Configuring Username and Password Pairs

•Configuring Multiple Privilege Levels

Default Password and Privilege Level Configuration

Table 6-1 shows the default password and privilege level configuration.

Table 6-1 Default Password and Privilege Levels 

Feature	Default Setting
Enable password and privilege level	No password is defined. The default is level 15 (privileged EXEC level). The password is not encrypted in the configuration file.
Enable secret password and privilege level	No password is defined. The default is level 15 (privileged EXEC level). The password is encrypted before it is written to the configuration file.
Line password	No password is defined.

Setting or Changing a Static Enable Password

The enable password controls access to the privileged EXEC mode. Beginning in privileged EXEC mode, follow these steps to set or change a static enable password:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	enable password password	Define a new password or change an existing password for access to privileged EXEC mode. By default, no password is defined. For password, specify a string from 1 to 25 alphanumeric characters. The string cannot start with a number, is case sensitive, and allows spaces but ignores leading spaces. It can contain the question mark (?) character if you precede the question mark with the key combination Crtl-v when you create the password; for example, to create the password abc?123, do this: Enter abc. Enter Crtl-v. Enter ?123. When the system prompts you to enter the enable password, you need not precede the question mark with the Ctrl-v; you can simply enter abc?123 at the password prompt.
Step 3	end	Return to privileged EXEC mode.
Step 4	show running-config	Verify your entries.
Step 5	copy running-config startup-config	(Optional) Save your entries in the configuration file. The enable password is not encrypted and can be read in the switch configuration file.

To remove the password, use the no enable password global configuration command.

This example shows how to change the enable password to l1u2c3k4y5. The password is not encrypted and provides access to level 15 (traditional privileged EXEC mode access):

Switch(config)# enable password l1u2c3k4y5

Protecting Enable and Enable Secret Passwords with Encryption

To provide an additional layer of security, particularly for passwords that cross the network or that are stored on a Trivial File Transfer Protocol (TFTP) server, you can use either the enable password or enable secret commands. Both commands accomplish the same thing; that is, you can establish an encrypted password that users must enter to access privileged EXEC mode (the default) or any privilege level you specify.

We recommend that you use the enable secret command because it uses an improved encryption algorithm.

If you configure the enable secret command, it takes precedence over the enable password command; the two commands cannot be in effect simultaneously.

Beginning in privileged EXEC mode, follow these steps to configure encryption for enable and enable secret passwords:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	enable password [level level] {password | encryption-type encrypted-password} or enable secret [level level] {password | encryption-type encrypted-password}	Define a new password or change an existing password for access to privileged EXEC mode. or Define a secret password, which is saved using a nonreversible encryption method. (Optional) For level, the range is from 0 to 15. Level 1 is normal user EXEC mode privileges. The default level is 15 (privileged EXEC mode privileges). For password, specify a string from 1 to 25 alphanumeric characters. The string cannot start with a number, is case sensitive, and allows spaces but ignores leading spaces. By default, no password is defined. (Optional) For encryption-type, only type 5, a Cisco proprietary encryption algorithm, is available. If you specify an encryption type, you must provide an encrypted password—an encrypted password you copy from another Catalyst 3550 multilayer switch configuration. Note If you specify an encryption type and then enter a clear text password, you can not re-enter privileged EXEC mode. You cannot recover a lost encrypted password by any method.
Step 3	service password-encryption	(Optional) Encrypt the password when the password is defined or when the current configuration is written. Encryption prevents the password from being readable in the configuration file.
Step 4	end	Return to privileged EXEC mode.
Step 5	copy running-config startup-config	(Optional) Save your entries in the configuration file.

If both the enable and enable secret passwords are defined, users must enter the enable secret password.

Use the level keyword to define a password for a specific privilege level. After you specify the level and set a password, give the password only to users who need to have access at this level. Use the privilege level global configuration command to specify commands accessible at various levels. For more information, see the "Configuring Multiple Privilege Levels" section.

If you enable password encryption, it applies to all passwords including username passwords, authentication key passwords, the privileged command password, and console and virtual terminal line passwords.

To remove a password and level, use the no enable password [level level] or no enable secret [level level] global configuration command. To disable password encryption, use the no service password-encryption global configuration command.

This example shows how to configure the encrypted password $1$FaD0$Xyti5Rkls3LoyxzS8 for privilege level 2:

Switch(config)# enable secret level 2 5 $1$FaD0$Xyti5Rkls3LoyxzS8

Setting a Telnet Password for a Terminal Line

When you power-up your switch for the first time, an automatic setup program runs to assign IP information and to create a default configuration for continued use. The setup program also prompts you to configure your switch for Telnet access through a password. If you neglected to configure this password during the setup program, you can configure it now through the command-line interface (CLI).

Beginning in privileged EXEC mode, follow these steps to configure your switch for Telnet access:

	Command	Purpose
Step 1		Attach a PC or workstation with emulation software to the switch console port. The default data characteristics of the console port are 9600, 8, 1, no parity. You might need to press the Return key several times to see the command-line prompt.
Step 2	enable password password	Enter privileged EXEC mode.
Step 3	configure terminal	Enter global configuration mode.
Step 4	line vty 0 15	Configure the number of Telnet sessions (lines). There are 16 possible sessions on a command-capable switch. The 0 and 15 mean that you are configuring all 16 possible Telnet sessions.
Step 5	password password	Enter a Telnet password for the line or lines. For password, specify a string from 1 to 25 alphanumeric characters. The string cannot start with a number, is case sensitive, and allows spaces but ignores leading spaces. By default, no password is defined.
Step 6	end	Return to privileged EXEC mode.
Step 7	show running-config	Verify your entries. The password is listed under the command line vty 0 15.
Step 8	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To remove the password, use the no password global configuration command.

This example shows how to set the Telnet password to let45me67in89:

Switch(config)# line vty 10

Switch(config-line)# password let45me67in89

Configuring Username and Password Pairs

You can configure username and password pairs, which are locally stored on the switch. These pairs are assigned to lines or interfaces and authenticate each user before that user can access the switch. If you have defined privilege levels, you can also assign a specific privilege level (with associated rights and privileges) to each username and password pair.

Beginning in privileged EXEC mode, follow these steps to establish a username-based authentication system that requests a username and password during switch login operations:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	username name [privilege level] {password encryption-type password}	Enter the username, privilege level, and password for each user. For name, specify the user ID as one word. Spaces and quotation marks are not allowed. (Optional) For level, specify the privilege level the user has after gaining access. The range is 0 to 15. Level 15 gives privileged EXEC mode access. Level 1 gives user EXEC mode access. For encryption-type, enter 0 to specify that an unencrypted password will follow. Enter 7 to specify that a hidden password will follow. For password, specify the password the user must enter to gain access to the switch. The password must be from 1 to 25 characters, can contain embedded spaces, and must be the last option specified in the username command.
Step 3	line console 0 or line vty 0 15	Enter line configuration mode, and configure the console port (line 0) or the VTY lines (line 0 to 15).
Step 4	login local	Enable local password checking at login time. Authentication is based on the username specified in Step 2.
Step 5	end	Return to privileged EXEC mode.
Step 6	show running-config	Verify your entries.
Step 7	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To disable username authentication for a specific user, use the no username name global configuration command. To disable password checking and allow connections without a password, use the no login line configuration command.

Configuring Multiple Privilege Levels

By default, the IOS software has two modes of password security: user EXEC and privileged EXEC. You can configure up to 16 hierarchical levels of commands for each mode. By configuring multiple passwords, you can allow different sets of users to have access to specified commands.

For example, if you want many users to have access to the clear line command, you can assign it level 2 security and distribute the level 2 password fairly widely. But if you want more restricted access to the configure command, you can assign it level 3 security and distribute that password to a more restricted group of users.

This section includes this configuration information:

•Setting the Privilege Level for a Command

•Changing the Default Privilege Level for Lines

•Logging into and Exiting a Privilege Level

Setting the Privilege Level for a Command

Beginning in privileged EXEC mode, follow these steps to set the privilege level for a command mode:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	privilege mode level level command	Set the privilege level for a command. For mode, enter configure for global configuration mode, exec for EXEC mode, interface for interface configuration mode, or line for line configuration mode. For level, the range is from 0 to 15. Level 1 is for normal user EXEC mode privileges. Level 15 is the level of access permitted by the enable password. For command, specify the command to which you want to restrict access.
Step 3	enable password level level password	Specify the enable password for the privilege level. For level, the range is from 0 to 15. Level 1 is for normal user EXEC mode privileges. For password, specify a string from 1 to 25 alphanumeric characters. The string cannot start with a number, is case sensitive, and allows spaces but ignores leading spaces. By default, no password is defined.
Step 4	end	Return to privileged EXEC mode.
Step 5	show running-config or show privilege	Verify your entries. The first command displays the password and access level configuration. The second command displays the privilege level configuration.
Step 6	copy running-config startup-config	(Optional) Save your entries in the configuration file.

When you set a command to a privilege level, all commands whose syntax is a subset of that command are also set to that level. For example, if you set the show ip route command to level 15, the show commands and show ip commands are automatically set to privilege level 15 unless you set them individually to different levels.

To return to the default privilege for a given command, use the no privilege mode level level command global configuration command.

This example shows how to set the configure command to privilege level 14 and define SecretPswd14 as the password users must enter to use level 14 commands:

Switch(config)# privilege exec level 14 configure

Switch(config)# enable password level 14 SecretPswd14

Changing the Default Privilege Level for Lines

Beginning in privileged EXEC mode, follow these steps to change the default privilege level for a line:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	line vty line	Select the virtual terminal line on which to restrict access.
Step 3	privilege level level	Change the default privilege level for the line. For level, the range is from 0 to 15. Level 1 is for normal user EXEC mode privileges. Level 15 is the level of access permitted by the enable password.
Step 4	end	Return to privileged EXEC mode.
Step 5	show running-config or show privilege	Verify your entries. The first command displays the password and access level configuration. The second command displays the privilege level configuration.
Step 6	copy running-config startup-config	(Optional) Save your entries in the configuration file.

Users can override the privilege level you set using the privilege level line configuration command by logging in to the line and enabling a different privilege level. They can lower the privilege level by using the disable command. If users know the password to a higher privilege level, they can use that password to enable the higher privilege level. You might specify a high level or privilege level for your console line to restrict line usage.

To return to the default line privilege level, use the no privilege level line configuration command.

Logging into and Exiting a Privilege Level

Beginning in privileged EXEC mode, follow these steps to log in to a specified privilege level and to exit to a specified privilege level:

	Command	Purpose
Step 1	enable level	Log in to a specified privilege level. For level, the range is 0 to 15.
Step 2	disable level	Exit to a specified privilege level. For level, the range is 0 to 15.

Controlling Switch Access with TACACS+

This section describes how to enable and configure Terminal Access Controller Access Control System Plus (TACACS+), which provides detailed accounting information and flexible administrative control over authentication and authorization processes. TACACS+ is facilitated through (authentication, authorization, accounting (AAA)) and can be enabled only through AAA commands.

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Note For complete syntax and usage information for the commands used in this section, refer to the Cisco IOS Security Command Reference for Release 12.1.

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This section contains this configuration information:

•Understanding TACACS+

•TACACS+ Operation

•Configuring TACACS+

•Displaying the TACACS+ Configuration

Understanding TACACS+

TACACS+ is a security application that provides centralized validation of users attempting to gain access to your switch. TACACS+ services are maintained in a database on a TACACS+ daemon typically running on a UNIX or Windows NT workstation. You should have access to and should configure a TACACS+ server before the configuring TACACS+ features on your switch.

TACACS+ provides for separate and modular authentication, authorization, and accounting facilities. TACACS+ allows for a single access control server (the TACACS+ daemon) to provide each service—authentication, authorization, and accounting—independently. Each service can be tied into its own database to take advantage of other services available on that server or on the network, depending on the capabilities of the daemon.

The goal of TACACS+ is to provide a method for managing multiple network access points from a single management service. Your switch can be a network access server along with other Cisco routers and access servers. A network access server provides connections to a single user, to a network or subnetwork, and to interconnected networks as shown in Figure 6-1.

Figure 6-1 Typical TACACS+ Network Configuration

TACACS+, administered through the AAA security services, can provide these services:

•Authentication—Provides complete control of authentication through login and password dialog, challenge and response, and messaging support.

The authentication facility can conduct a dialog with the user (for example, after a username and password are provided, to challenge a user with a number of questions, such as home address, mother's maiden name, service type, and social security number). In addition, the TACACS+ authentication service can also send messages to user screens. For example, a message could notify users that their passwords must be changed because of the company's password aging policy.

•Authorization—Provides fine-grained control over user capabilities for the duration of the user's session, including but not limited to setting autocommands, access control, session duration, or protocol support. You can also enforce restrictions on what commands a user can execute with the TACACS+ authorization feature.

•Accounting—Collects and sends information used for billing, auditing, and reporting to the TACACS+ daemon. Network managers can use the accounting facility to track user activity for a security audit or to provide information for user billing. Accounting records include user identities, start and stop times, executed commands (such as PPP), number of packets, and number of bytes.

The TACACS+ protocol provides authentication between the switch and the TACACS+ daemon, and it ensures confidentiality because all protocol exchanges between the switch and the TACACS+ daemon are encrypted.

You need a system running the TACACS+ daemon software to use TACACS+ on your switch.

TACACS+ Operation

When a user attempts a simple ASCII login by authenticating to a switch using TACACS+, this process occurs:

1. When the connection is established, the switch contacts the TACACS+ daemon to obtain a username prompt, which is then displayed to the user. The user enters a username, and the switch then contacts the TACACS+ daemon to obtain a password prompt. The switch displays the password prompt to the user, the user enters a password, and the password is then sent to the TACACS+ daemon.

TACACS+ allows a conversation to be held between the daemon and the user until the daemon receives enough information to authenticate the user. The daemon prompts for a username and password combination, but can include other items, such as the user's mother's maiden name.

2. The switch eventually receives one of these responses from the TACACS+ daemon:

–ACCEPT—The user is authenticated and service can begin. If the switch is configured to require authorization, authorization begins at this time.

–REJECT—The user has failed to authenticate. The user can be denied further access or is prompted to retry the login sequence, depending on the TACACS+ daemon.

–ERROR—An error occurred at some time during authentication with the daemon or in the network connection between the daemon and the switch. If an ERROR response is received, the switch typically tries to use an alternative method for authenticating the user.

–CONTINUE—The user is prompted for additional authentication information.

Following authentication, the user undergoes an additional authorization phase if authorization has been enabled on the switch. Users must first successfully complete TACACS+ authentication before proceeding to TACACS+ authorization.

3. If TACACS+ authorization is required, the TACACS+ daemon is again contacted, and it returns an ACCEPT or REJECT authorization response. If an ACCEPT response is returned, the response contains data in the form of attributes that direct the EXEC or NETWORK session for that user, determining the services that the user can access:

–Telnet, rlogin, or EXEC services

–Connection parameters, including the host or client IP address, access list, and user timeouts

Configuring TACACS+

This section describes how to configure your switch to support TACACS+. At a minimum, you must identify the host or hosts maintaining the TACACS+ daemon and define the method lists for TACACS+ authentication. You can optionally define method lists for TACACS+ authorization and accounting. A method list defines the sequence and methods to be used to authenticate, to authorize, or to keep accounts on a user. You can use method lists to designate one or more security protocols to be used, thus ensuring a backup system if the initial method fails. The software uses the first method listed to authenticate, to authorize, or to keep accounts on users; if that method does not respond, the software selects the next method in the list. This process continues until there is successful communication with a listed method or the method list is exhausted.

This section contains this configuration information:

•Default TACACS+ Configuration

•Identifying the TACACS+ Server Host and Setting the Authentication Key

•Configuring Login Authentication

•Configuring TACACS+ Authorization for EXEC Access and Network Services

•Starting TACACS+ Accounting

•Configuring the Switch for Local Authentication and Authorization

Default TACACS+ Configuration

TACACS+ and AAA are disabled by default.

To prevent a lapse in security, you cannot configure TACACS+ through a network management application.When enabled, TACACS+ can authenticate users accessing the switch through the CLI.

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Note Although TACACS+ configuration is performed through the CLI, the TACACS+ server authenticates HTTP connections that have been configured with a privilege level of 15.

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Identifying the TACACS+ Server Host and Setting the Authentication Key

You can configure the switch to use a single server or AAA server groups to group existing server hosts for authentication. You can group servers to select a subset of the configured server hosts and use them for a particular service. The server group is used with a global server-host list and contains the list of IP addresses of the selected server hosts.

Beginning in privileged EXEC mode, follow these steps to identify the IP host or host maintaining TACACS+ server and optionally set the encryption key:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	tacacs-server host hostname [port integer] [timeout integer] [key string]	Identify the IP host or hosts maintaining a TACACS+ server. Enter this command multiple times to create a list of preferred hosts. The software searches for hosts in the order in which you specify them. For hostname, specify the name or IP address of the host. (Optional) For port integer, specify a server port number. The default is port 49. The range is 1 to 65535. (Optional) For timeout integer, specify a time in seconds the switch waits for a response from the daemon before it times out and declares an error. The default is 5 seconds. The range is 1 to 1000 seconds. (Optional) For key string, specify the encryption key for encrypting and decrypting all traffic between the switch and the TACACS+ daemon. You must configure the same key on the TACACS+ daemon for encryption to be successful.
Step 3	aaa group server tacacs+ group-name	(Optional) Define the AAA server-group with a group name. This command puts the switch in a server group subconfiguration mode.
Step 4	server ip-address	(Optional) Associate a particular TACACS+ server with the defined server group. Repeat this step for each TACACS+ server in the AAA server group. Each server in the group must be previously defined in Step 2.
Step 5	end	Return to privileged EXEC mode.
Step 6	show tacacs	Verify your entries.
Step 7	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To remove the specified TACACS+ server name or address, use the no tacacs-server host hostname global configuration command. To remove a server group from the configuration list, use the no aaa group server tacacs+ group-name global configuration command. To remove the IP address of a TACACS+ server, use the no server ip-address server group subconfiguration command.

Configuring Login Authentication

To configure AAA authentication, you define a named list of authentication methods and then apply that list to various interfaces. The method list defines the types of authentication to be performed and the sequence in which they are performed; it must be applied to a specific interface before any of the defined authentication methods are performed. The only exception is the default method list (which, by coincidence, is named default). The default method list is automatically applied to all interfaces except those that have a named method list explicitly defined. A defined method list overrides the default method list.

A method list describes the sequence and authentication methods to be queried to authenticate a user. You can designate one or more security protocols to be used for authentication, thus ensuring a backup system for authentication in case the initial method fails. The software uses the first method listed to authenticate users; if that method fails to respond, the software selects the next authentication method in the method list. This process continues until there is successful communication with a listed authentication method or until all defined methods are exhausted. If authentication fails at any point in this cycle—meaning that the security server or local username database responds by denying the user access—the authentication process stops, and no other authentication methods are attempted.

Beginning in privileged EXEC mode, follow these steps to configure login authentication:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	aaa new-model	Enable AAA.
Step 3	aaa authentication login {default | list-name} method1 [method2...]	Create a login authentication method list. To create a default list that is used when a named list is not specified in the login authentication command, use the default keyword followed by the methods that are to be used in default situations. The default method list is automatically applied to all interfaces. For list-name, specify a character string to name the list you are creating. For method1..., specify the actual method the authentication algorithm tries. The additional methods of authentication are used only if the previous method returns an error, not if it fails. Select one of these methods: line—Use the line password for authentication. You must define a line password before you can use this authentication method. Use the password password line configuration command. local—Use the local username database for authentication. You must enter username information into the database. Use the username password global configuration command. tacacs+—Uses TACACS+ authentication. You must configure the TACACS+ server before you can use this authentication method.
Step 4	line [console | tty | vty] line-number [ending-line-number]	Enter line configuration mode, and configure the lines to which you want to apply the authentication list.
Step 5	login authentication {default | list-name}	Apply the authentication list to a line or set of lines. If you specify default, use the default list created with the aaa authentication login command. For list-name, specify the list created with the aaa authentication login command.
Step 6	end	Return to privileged EXEC mode.
Step 7	show running-config	Verify your entries.
Step 8	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To disable AAA, use the no aaa new-model global configuration command. To disable AAA authentication, use the no aaa authentication login {default | list-name} method1 [method2...] global configuration command. To either disable TACACS+ authentication for logins or to return to the default value, use the no login authentication {default | list-name}line configuration command.

Configuring TACACS+ Authorization for EXEC Access and Network Services

AAA authorization limits the services available to a user. When AAA authorization is enabled, the switch uses information retrieved from the user's profile, which is located either in the local user database or on the security server, to configure the user's session. The user is granted access to a requested service only if the information in the user profile allows it.

You can use the aaa authorization command with the tacacs+ keyword to set parameters that restrict a user's network access to privileged EXEC mode (EXEC access).

The aaa authorization exec tacacs+ local command sets these authorization parameters:

•Use TACACS+ for EXEC access authorization if authentication was performed by using TACACS+.

•Use the local database if authentication was not performed by using TACACS+.

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Note Authorization is bypassed for authenticated users who log in through the CLI even if authorization has been configured.

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Beginning in privileged EXEC mode, follow these steps to specify TACACS+ authorization for EXEC access and network services:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	aaa authorization network tacacs+	Configure the switch for user TACACS+ authorization for all network-related service requests.
Step 3	aaa authorization exec tacacs+	Configure the switch for user TACACS+ authorization to determine if the user has EXEC access. The exec keyword might return user profile information (such as autocommand information).
Step 4	end	Return to privileged EXEC mode.
Step 5	show running-config	Verify your entries.
Step 6	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To disable authorization, use the no aaa authorization {network | exec} method1 global configuration command.

Starting TACACS+ Accounting

The AAA accounting feature tracks the services that users are accessing as well as the amount of network resources they are consuming. When AAA accounting is enabled, the switch reports user activity to the TACACS+ security server in the form of accounting records. Each accounting record contains accounting attribute-value (AV) pairs and is stored on the security server. This data can then be analyzed for network management, client billing, or auditing.

Beginning in privileged EXEC mode, follow these steps to enable TACACS+ accounting for each Cisco IOS privilege level and for network services:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	aaa accounting network start-stop tacacs+	Enable TACACS+ accounting for all network-related service requests.
Step 3	aaa accounting exec start-stop tacacs+	Enable TACACS+ accounting to send a start-record accounting notice at the beginning of an EXEC process and a stop-record at the end.
Step 4	end	Return to privileged EXEC mode.
Step 5	show running-config	Verify your entries.
Step 6	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To disable accounting, use the no aaa accounting {network | exec}{start-stop} method1... global configuration command.

Configuring the Switch for Local Authentication and Authorization

You can configure AAA to operate without a server by setting the switch to implement AAA in local mode. The switch then handles authentication and authorization. No accounting is available in this configuration.

Beginning in privileged EXEC mode, follow these steps to configure the switch for local AAA:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	aaa new-model	Enable AAA.
Step 3	aaa authentication login default local	Set the login authentication to use the local username database. The default keyword applies the local user database authentication to all interfaces.
Step 4	aaa authorization exec local	Configure user AAA authorization to determine if the user is allowed to run an EXEC shell by checking the local database.
Step 5	aaa authorization network local	Configure user AAA authorization for all network-related service requests.
Step 6	username name [privilege level] {password encryption-type password}	Enter the local database, and establish a username-based authentication system. Repeat this command for each user. For name, specify the user ID as one word. Spaces and quotation marks are not allowed. (Optional) For level, specify the privilege level the user has after gaining access. The range is 0 to 15. Level 15 gives privileged EXEC mode access. Level 0 gives user EXEC mode access. For encryption-type, enter 0 to specify that an unencrypted password follows. Enter 7 to specify that a hidden password follows. For password, specify the password the user must enter to gain access to the switch. The password must be from 1 to 25 characters, can contain embedded spaces, and must be the last option specified in the username command.
Step 7	end	Return to privileged EXEC mode.
Step 8	show running-config	Verify your entries.
Step 9	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To disable AAA, use the no aaa new-model global configuration command. To disable authorization, use the no aaa authorization {network | exec} method1 global configuration command.

Displaying the TACACS+ Configuration

To display TACACS+ server statistics, use the show tacacs privileged EXEC command.

Managing the System Time and Date

You can manage the system time and date on your switch using automatic, such as the Network Time Protocol (NTP), or manual configuration methods.

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Note For complete syntax and usage information for the commands used in this section, refer to the Cisco IOS Configuration Fundamentals Command Reference for Release 12.1.

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This section contains this configuration information:

•Understanding the System Clock

•Understanding Network Time Protocol

•Configuring NTP

•Configuring Time and Date Manually

Understanding the System Clock

The heart of the time service is the system clock. This clock runs from the moment the system starts up and keeps track of the current date and time.

The system clock can then be set from these sources:

•Network Time Protocol

•Manual configuration

The system clock can provide time to these services:

•User show commands

•Logging and debugging messages

The system clock keeps track of time internally based on Universal Time Coordinated (UTC), also known as Greenwich Mean Time (GMT). You can configure information about the local time zone and summer time (daylight saving time) so that the time is correctly displayed for the local time zone.

The system clock keeps track of whether the time is authoritative or not (that is, whether it has been set by a time source considered to be authoritative). If it is not authoritative, the time is available only for display purposes and is not redistributed. For configuration information, see the "Configuring Time and Date Manually" section.

Understanding Network Time Protocol

The NTP is designed to time-synchronize a network of devices. NTP runs over User Datagram Protocol (UDP), which runs over IP. NTP is documented in RFC 1305.

An NTP network usually gets its time from an authoritative time source, such as a radio clock or an atomic clock attached to a time server. NTP then distributes this time across the network. NTP is extremely efficient; no more than one packet per minute is necessary to synchronize two devices to within a millisecond of one another.

NTP uses the concept of a stratum to describe how many NTP hops away a device is from an authoritative time source. A stratum 1 time server has a radio or atomic clock directly attached, a stratum 2 time server receives its time through NTP from a stratum 1 time server, and so on. A device running NTP automatically chooses as its time source the device with the lowest stratum number with which it communicates through NTP. This strategy effectively builds a self-organizing tree of NTP speakers.

NTP avoids synchronizing to a device whose time might not be accurate by never synchronizing to a device that is not synchronized. NTP also compares the time reported by several devices and does not synchronize to a device whose time is significantly different than the others, even if its stratum is lower.

The communications between devices running NTP (known as associations) are usually statically configured; each device is given the IP address of all devices with which it should form associations. Accurate timekeeping is possible by exchanging NTP messages between each pair of devices with an association. However, in a LAN environment, NTP can be configured to use IP broadcast messages instead. This alternative reduces configuration complexity because each device can simply be configured to send or receive broadcast messages. However, in that case, information flow is one-way only.

The time kept on a device is a critical resource; you should use the security features of NTP to avoid the accidental or malicious setting of an incorrect time. Two mechanisms are available: an access list-based restriction scheme and an encrypted authentication mechanism.

Cisco's implementation of NTP does not support stratum 1 service; it is not possible to connect to a radio or atomic clock. We recommend that the time service for your network be derived from the public NTP servers available on the IP Internet. Figure 6-2 show a typical network example using NTP.

If the network is isolated from the Internet, Cisco's implementation of NTP allows a device to act as though it is synchronized through NTP, when in fact it has determined the time by using other means. Other devices then synchronize to that device through NTP.

When multiple sources of time are available, NTP is always considered to be more authoritative. NTP time overrides the time set by any other method.

A number of manufacturers include NTP software for their host systems, and a publicly available version for systems running UNIX and its various derivatives is also available. This software allows host systems to be time-synchronized as well.

Figure 6-2 Typical NTP Network Configuration

Configuring NTP

The Catalyst 3550 switches do not have a hardware-supported clock, and they cannot function as an NTP master clock to which peers synchronize themselves when an external NTP source is not available. These switches also have no hardware support for a calendar. As a result, the ntp update-calendar and the ntp master global configuration commands are not available.

This section contains this configuration information:

•Default NTP Configuration

•Configuring NTP Authentication

•Configuring NTP Associations

•Configuring NTP Broadcast Service

•Configuring NTP Access Restrictions

•Configuring the Source IP Address for NTP Packets

•Displaying the NTP Configuration

Default NTP Configuration

Table 6-2 shows the default NTP configuration.

Table 6-2 Default NTP Configuration 

Feature	Default Setting
NTP authentication	Disabled. No authentication key is specified.
NTP peer or server associations	None configured.
NTP broadcast service	Disabled; no interface sends or receives NTP broadcast packets.
NTP access restrictions	No access control is specified.
NTP packet source IP address	The source address is determined by the outgoing interface.

NTP is enabled on all interfaces by default. All interfaces receive NTP packets.

Configuring NTP Authentication

This procedure must be coordinated with the administrator of the NTP server; the information you configure in this procedure must be matched by the servers used by the switch to synchronize its time to the NTP server.

Beginning in privileged EXEC mode, follow these steps to authenticate the associations (communications between devices running NTP that provide for accurate timekeeping) with other devices for security purposes:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	ntp authenticate	Enable the NTP authentication feature, which is disabled by default.
Step 3	ntp authentication-key number md5 value	Define the authentication keys. By default, none are defined. For number, specify a key number. The range is 1 to 4294967295. md5 specifies that message authentication support is provided by using the message digest algorithm 5 (MD5). For value, enter an arbitrary string of up to eight characters for the key. The switch does not synchronize to a device unless both have one of these authentication keys, and the key number is specified by the ntp trusted-key key-number command.
Step 4	ntp trusted-key key-number	Specify one or more key numbers (defined in Step 3) that a peer NTP device must provide in its NTP packets for this switch to synchronize to it. By default, no trusted keys are defined. For key-number, specify the key defined in Step 3. This command provides protection against accidentally synchronizing the switch to a device that is not trusted.
Step 5	end	Return to privileged EXEC mode.
Step 6	show running-config	Verify your entries.
Step 7	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To disable NTP authentication, use the no ntp authenticate global configuration command. To remove an authentication key, use the no ntp authentication-key number global configuration command. To disable authentication of the identity of a device, use the no ntp trusted-key key-number global configuration command.

This example shows how to configure the switch to synchronize only to devices providing authentication key 42 in the device's NTP packets:

Switch(config)# ntp authenticate

Switch(config)# ntp authentication-key 42 md5 aNiceKey

Switch(config)# ntp trusted-key 42

Configuring NTP Associations