Catalyst 4500 Series Switch Software Configuration Guide, IOS XE 3.7.xE and IOS 15.2(3)Ex

About DHCP-Based Autoconfiguration

Note Starting with Release 12.2(20)EW, you can enable DHCP AutoConfiguration by entering the write erase command. This command clears the startup-config in NVRAM. In images prior to Release 12.2(20)EW, this command does not enable autoconfiguration.

DHCP provides configuration information to Internet hosts and internetworking devices. This protocol consists of two components: one component for delivering configuration parameters from a DHCP server to a device and another component that is a mechanism for allocating network addresses to devices. DHCP is built on a client-server model, in which designated DHCP servers allocate network addresses and deliver configuration parameters to dynamically configured devices. The switch can act as both a DHCP client and a DHCP server.

With DHCP-based autoconfiguration, no DHCP client-side configuration is needed on your switch because your switch (the DHCP client) is automatically configured at startup with IP address information and a configuration file. However, you need to configure the DHCP server or the DHCP server feature on your switch for various lease options associated with IP addresses. If you are using DHCP to relay the configuration file location on the network, you might also need to configure a Trivial File Transfer Protocol (TFTP) server and a Domain Name System (DNS) server.

DHCP-based autoconfiguration replaces the BOOTP client functionality on your switch.

DHCP Client Request Process

At startup the switch automatically requests configuration information from a DHCP server if a configuration file is not present on the switch.

Figure 3-1 shows the sequence of messages that are exchanged between the DHCP client and the DHCP server.

Figure 3-1 DHCP Client and Server Message Exchange

The client, Switch A, broadcasts a DHCPDISCOVER message to locate a DHCP server. The DHCP server offers configuration parameters (such as an IP address, subnet mask, gateway IP address, DNS IP address, lease for the IP address, and so forth) to the client in a DHCPOFFER unicast message.

In a DHCPREQUEST broadcast message, the client returns a formal request for the offered configuration information to the DHCP server. The formal request is broadcast so that all other DHCP servers that received the DHCPDISCOVER broadcast message from the client can reclaim the IP addresses that they offered to the client.

The DHCP server confirms that the IP address has been allocated to the client by returning a DHCPACK unicast message to the client. With this message, the client and server are bound, and the client uses the configuration information that it received from the server. The amount of information the switch receives depends on how you configure the DHCP server. For more information, see the “Configuring the DHCP Server” section.

If the configuration parameters sent to the client in the DHCPOFFER unicast message are invalid (if configuration error exists), the client returns a DHCPDECLINE broadcast message to the DHCP server.

The DHCP server sends the client a DHCPNAK denial broadcast message, which means that the offered configuration parameters have not been assigned, that an error has occurred during the negotiation of the parameters, or that the client has been slow in responding to the DHCPOFFER message. (The DHCP server might have assigned the parameters to another client.)

A DHCP client might receive offers from multiple DHCP servers and can accept any of them; however, the client usually accepts the first offer it receives. The offer from the DHCP server is not a guarantee that the IP address will be allocated to the client; however, the server usually reserves the address until the client has had a chance to formally request the address.

Troubleshooting Tips

Sometimes due to firmware upgrades or client VLAN configuration changes on the device, the DHCP client may send a DHCPREQUEST message with a cached IP address. If the DHCP server does not accept the request, the client may continue to send DHCPREQUEST messages instead of a DHCPDISCOVER message, and fail to get an IP address from the DHCP server.

To remedy this situation, use the renew deny unknown command in DHCP pool configuration mode. This command forces the DHCP server to reject renewal requests from clients and the DHCP server sends a DHCPNAK denial message to the client, forcing the client back to its initial state.

Configuring the DHCP Server

A switch can act as both the DHCP client and the DHCP server. By default, the Cisco IOS DHCP server and relay agent features are enabled on your switch.

You should configure the DHCP server, or the DHCP server feature running on your switch, with reserved leases that are bound to each switch by the switch hardware address.

If you want the switch to receive IP address information, you must configure the DHCP server with these lease options:

• IP address of the client (required)
• Subnet mask of the client (required)
• DNS server IP address (optional)
• Router IP address (required)

Note The router IP address is the default gateway address for the switch.

If you want the switch to receive the configuration file from a TFTP server, you must configure the DHCP server with these lease options:

• TFTP server name or IP address (required)
• Boot filename (the name of the configuration file that the client needs) (recommended)
• Host name (optional)

Depending on the settings of the DHCP server or the DHCP server feature running on your switch, the switch can receive IP address information, the configuration file, or both.

If you do not configure the DHCP server, or the DHCP server feature running on your switch, with the lease options described earlier, the switch replies to client requests with only those parameters that are configured. If the IP address and subnet mask are not in the reply, the switch is not configured. If the router IP address or TFTP server name (or IP address) are not found, the switch might send broadcast, instead of unicast, TFTP requests. Unavailability of other lease options does not impact autoconfiguration.

The DHCP server, or the DHCP server feature running on your switch, can be on the same LAN or on a different LAN than the switch. If the DHCP server is running on a different LAN, you should configure a DHCP relay, which forwards broadcast traffic between two directly connected LANs. A router does not forward broadcast packets, but it forwards packets based on the destination IP address in the received packet. For more information on relay devices, see the “Configuring the Relay Device” section.

Configuring the TFTP Server

Based on the DHCP server configuration, the switch attempts to download one or more configuration files from the TFTP server. If you configured the DHCP server to respond to the switch with all the options required for IP connectivity to the TFTP server, and if you configured the DHCP server with a TFTP server name, address, and configuration filename, the switch attempts to download the specified configuration file from the specified TFTP server.

If you did not specify the configuration filename or the TFTP server name, or if the configuration file could not be downloaded, the switch attempts to download a configuration file using various combinations of filenames and TFTP server addresses. The files include the specified configuration filename (if any) and the following files: network-confg, cisconet.cfg, hostname.confg, or hostname.cfg, where hostname is the current hostname of the switch and router-confg and ciscortr.cfg. The TFTP server addresses used include the specified TFTP server address (if any) and the broadcast address (255.255.255.255).

For the switch to successfully download a configuration file, the TFTP server must contain one or more configuration files in its base directory. The files can include the following:

• The configuration file named in the DHCP reply (the actual switch configuration file).
• The network-confg or the cisconet.cfg file (known as the default configuration files).
• The router-confg or the ciscortr.cfg file. (These files contain commands common to all switches. Normally, if the DHCP and TFTP servers are properly configured, these files are not accessed.)

If you specify the TFTP server name in the DHCP server-lease database, you must also configure the TFTP server name-to-IP-address mapping in the DNS-server database.

If the TFTP server you plan to use is on a different LAN from the switch, or if you plan to access it with the switch through the broadcast address (which occurs if the DHCP server response does not contain all the required information described earlier), you must configure a relay to forward the TFTP packets to the TFTP server. For more information, see the “Configuring the Relay Device” section. The preferred solution is to configure either the DHCP server or the DHCP server feature running on your switch with all the required information.

Configuring the DNS Server

The DHCP server, or the DHCP server feature running on your switch, uses the DNS server to resolve the TFTP server name to an IP address. You must configure the TFTP server name-to-IP address map on the DNS server. The TFTP server contains the configuration files for the switch.

You can configure the IP addresses of the DNS servers in the lease database of the DHCP server where the DHCP replies retrieve them. You can enter up to two DNS server IP addresses in the lease database.

The DNS server can be on the same or on a different LAN as the switch. If it is on a different LAN, the switch must be able to access it through a router.

Configuring the Relay Device

You must configure a relay device to forward received broadcast packets to the destination host whenever a switch sends broadcast packets to which a host on a different LAN must respond. Examples of such broadcast packets are DHCP, DNS, and in some cases, TFTP packets.

If the relay device is a Cisco router, enable IP routing (ip routing global configuration command) and configure helper addresses (ip helper-address interface configuration command). For example, in Figure 3-2, configure the router interfaces as follows:

On interface 10.0.0.2:

On interface 20.0.0.1:

Figure 3-2 Relay Device Used in Autoconfiguration

Obtaining Configuration Files

Depending on the availability of the IP address and the configuration filename in the DHCP reserved lease, the switch obtains its configuration information in these ways:

• The IP address and the configuration filename are reserved for the switch and provided in the DHCP reply (one-file read method).

The switch receives its IP address, subnet mask, TFTP server address, and the configuration filename from either the DHCP server or the DHCP server feature running on your switch. The switch sends a unicast message to the TFTP server to retrieve the named configuration file from the base directory of the server, and upon receipt, completes its boot-up process.

• The IP address and the configuration filename is reserved for the switch, but the TFTP server address is not provided in the DHCP reply (one-file read method).

The switch receives its IP address, subnet mask, and the configuration filename from either the DHCP server or the DHCP server feature running on your switch. The switch sends a broadcast message to a TFTP server to retrieve the named configuration file from the base directory of the server, and upon receipt, completes its boot-up process.

• Only the IP address is reserved for the switch and provided in the DHCP reply. The configuration filename is not provided (two-file read method).

The switch receives its IP address, subnet mask, and the TFTP server address from either the DHCP server or the DHCP server feature running on your switch. The switch sends a unicast message to the TFTP server to retrieve the network-confg or cisconet.cfg default configuration file. (If the network-confg file cannot be read, the switch reads the cisconet.cfg file.)

The default configuration file contains the host names-to-IP-address mapping for the switch. The switch fills its host table with the information in the file and obtains its host name. If the host name is not found in the file, the switch uses the host name in the DHCP reply. If the host name is not specified in the DHCP reply, the switch uses the default Switch as its host name.

After obtaining its host name from the default configuration file or the DHCP reply, the switch reads the configuration file that has the same name as its host name ( hostname -confg or hostname.cfg, depending on whether or not the network-confg file or the cisconet.cfg file was read earlier) from the TFTP server. If the cisconet.cfg file is read, the filename of the host is truncated to eight characters.

If the switch cannot read the network-confg, cisconet.cfg, or the hostname file, it reads the router-confg file. If the switch cannot read the router-confg file, it reads the ciscortr.cfg file.

Note The switch broadcasts TFTP server requests provided that one of these conditions is met: the TFTP server is not obtained from the DHCP replies; all attempts to read the configuration file through unicast transmissions fail; or the TFTP server name cannot be resolved to an IP address.

Example Configuration

Figure 3-3 shows a network example for retrieving IP information using DHCP-based autoconfiguration.

Figure 3-3 DHCP-Based Autoconfiguration Network Example

Table 3-2 shows the configuration of the reserved leases on either the DHCP server or the DHCP server feature running on your switch.

DNS Server Configuration

The DNS server maps the TFTP server name maritsu to IP address 10.0.0.3.

TFTP Server Configuration (on UNIX)

The TFTP server base directory is set to /tftpserver/work/. This directory contains the network-confg file used in the two-file read method. This file contains the host name that you plan to assign to the switch based on its IP address. The base directory also contains a configuration file for each switch ( switch1-confg, switch2-confg, and so forth) as shown in the following display:

DHCP Client Configuration

No configuration file is present on Switch 1 through Switch 4.

Configuration Explanation

In Figure 3-3, Switch 1 reads its configuration file as follows:

• Switch 1 obtains its IP address 10.0.0.21 from the DHCP server.
• If no configuration filename is given in the DHCP server reply, Switch 1 reads the network-confg file from the base directory of the TFTP server.
• Switch 1 adds the contents of the network-confg file to its host table.
• Switch 1 reads its host table by indexing its IP address 10.0.0.21 to its host name (switch1).
• Switch 1 reads the configuration file that corresponds to its host name; for example, it reads switch1-confg from the TFTP server.

Switches 2 through 4 retrieve their configuration files and IP addresses in the same way.

Using Configuration Mode to Configure Your Switch

To configure your switch from configuration mode, follow these steps:

Step 1 Connect a console terminal to the console interface of your supervisor engine.

Step 2 After a few seconds, you see the user EXEC prompt (Switch>). Now, you may want to enter privileged EXEC mode, also known as enable mode. Type enable to enter enable mode:

Note You must be in enable mode to make configuration changes.

The prompt changes to the enable prompt (#):

Step 3 At the enable prompt (#), enter the configure terminal command to enter global configuration mode:

Step 4 At the global configuration mode prompt, enter the interface type slot/interface command to enter interface configuration mode:

Step 5 In either of these configuration modes, enter changes to the switch configuration.

Step 6 Enter the end command to exit configuration mode.

Step 7 Save your settings. See the “Saving the Running Configuration Settings to Your Start-Up File” section.

Your switch is now minimally configured and can boot with the configuration you entered. To see a list of the configuration commands, enter ? at the prompt or press the help key in configuration mode.

Verifying the Running Configuration Settings

To verify the configuration settings you entered or the changes you made, enter the show running-config command at the enable prompt (#), as shown in this example:

Saving the Running Configuration Settings to Your Start-Up File

Caution This command saves the configuration settings that you created in configuration mode. If you fail to do this step, your configuration is lost the next time you reload the system.

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To store the configuration, changes to the configuration, or changes to the startup configuration in NVRAM, enter the copy running-config startup-config command at the enable prompt (#), as follows:

Reviewing the Configuration in NVRAM

To display information stored in NVRAM, enter the show startup-config EXEC command.

The following example shows a typical system configuration:

Configuring a Default Gateway

Note The switch uses the default gateway only when it is not configured with a routing protocol.

Configure a default gateway to send data to subnets other than its own when the switch is not configured with a routing protocol. The default gateway must be the IP address of an interface on a router that is directly connected to the switch.

To configure a default gateway, perform this task:

This example shows how to configure a default gateway and how to verify the configuration:

Configuring a Static Route

If your Telnet station or SNMP network management workstation is on a different network from your switch and a routing protocol has not been configured, you might need to add a static routing table entry for the network where your end station is located.

To configure a static route, perform this task:

This example shows how to use the ip route command to configure a static route to a workstation at IP address 171.10.5.10 on the switch with a subnet mask and IP address 172.20.3.35 of the forwarding router:

This example shows how to use the show running-config command to confirm the configuration of the static route:

This example shows how to use the ip route command to configure the static route IP address 171.20.5.3 with subnet mask and connected over VLAN 1 to a workstation on the switch:

This example shows how to use the show running-config command to confirm the configuration of the static route:

Setting or Changing a Static enable Password

To set or change a static password that controls access to the enable mode, enter this command:

This example shows how to configure an enable password as lab:

For instructions on how to display the password or access level configuration, see the “Displaying the Password, Access Level, and Privilege Level Configuration” section.

Using the enable password and enable secret Commands

To provide an additional layer of security, particularly for passwords that cross the network or that are stored on a TFTP server, use either the enable password or enable secret command. Both commands configure an encrypted password that you must enter to access the enable mode (the default) or any other privilege level that you specify.

We recommend that you use the enable secret command.

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

To configure the switch to require an enable password, enter one of these commands:

When you enter either of these password commands with the level option, you 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 configuration command to specify commands accessible at various levels.

If you enable the service password-encryption command, the password you enter is encrypted. When you display the password with the more system:running-config command, the password displays the password in encrypted form.

If you specify an encryption type, you must provide an encrypted password—an encrypted password you copy from another switch configuration.

Note You cannot recover a lost encrypted password. You must clear NVRAM and set a new password. See the “Recovering a Lost Enable Password” section for more information.

For information on how to display the password or access level configuration, see the “Displaying the Password, Access Level, and Privilege Level Configuration” section.

Setting or Changing a Privileged Password

To set or change a privileged password, enter this command:

For information on how to display the password or access level configuration, see the “Displaying the Password, Access Level, and Privilege Level Configuration” section.

Controlling Switch Access with TACACS+

This section describes how to enable and configure 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.

Note For complete syntax and usage information for the commands used in this section, see the Cisco IOS Security Command Reference, Release 12.2.

This section contains the following 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 configuring TACACS+ features on your switch.

TACACS+ provides for separate and modular AAA 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 locked 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 3-4.

Figure 3-4 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 (such as, after a username and password are provided, to challenge a user with several questions such as home address, mother’s maiden name, service type, and social security number). 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 strict 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 the 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 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 is not authenticated. The user can be denied 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.

After 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 and the services that the user can access:

• Telnet, Secure Shell (SSH), rlogin, or privileged 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 used to authenticate, to authorize, or to keep accounts on a user. Use method lists to designate one or more security protocols, 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 the following configuration information:

• Default TACACS+ Configuration
• Identifying the TACACS+ Server Host and Setting the Authentication Key
• Configuring TACACS+ Login Authentication
• Configuring TACACS+ Authorization for Privileged EXEC Access and Network Services
• Starting TACACS+ Accounting

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.

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.

Identifying the TACACS+ Server Host and Setting the Authentication Key

You can configure the switch to use a single server or AAA server groups in order 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.

To identify the IP host or host maintaining TACACS+ server and optionally set the encryption key, perform this task, beginning in privileged EXEC mode:

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 TACACS+ Login Authentication

To configure AAA authentication, define a named list of authentication methods and then apply that list to various ports. The method list defines the types of authentication you intend to perform and the sequence in which you intend to perform them; you must apply the list to a specific port before you can perform any of the defined authentication methods. The only exception is the default method list (which, by coincidence, is named default). The default method list is automatically applied to all ports 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 that must be queried to authenticate a user. You can designate one or more security protocols for authentication, 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.

To configure login authentication, perform this task, beginning in privileged EXEC mode:

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 Privileged 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.

To set parameters that restrict a user’s network access to privileged EXEC mode, use the aaa authorization global configuration command with the tacacs+ keyword.

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

• Use TACACS+ for privileged EXEC access authorization if authentication was performed by using TACACS+.
• Use the local database if authentication was not performed by using TACACS+.

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

To specify TACACS+ authorization for privileged EXEC access and network services, perform this task, beginning in privileged EXEC mode:

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 and the amount of network resources that 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.

To enable TACACS+ accounting for each Cisco IOS privilege level and for network services, perform this task, beginning in privileged EXEC mode:

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

Displaying the TACACS+ Configuration

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

Encrypting Passwords

Because protocol analyzers can examine packets (and read passwords), you can increase access security by configuring the Cisco IOS software to encrypt passwords. Encryption prevents the password from being readable in the configuration file.

To configure the Cisco IOS software to encrypt passwords, enter this command:

Encryption occurs when the current configuration is written or when a password is configured. Password encryption is applied to all passwords, including authentication key passwords, the privileged command password, console and virtual terminal line access passwords, and Border Gateway Protocol (BGP) neighbor passwords. The service password-encryption command keeps unauthorized individuals from viewing your password in your configuration file.

Caution The service password-encryption command does not provide a high-level of network security. If you use this command, you should also take additional network security measures.

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Although you cannot recover a lost encrypted password (that is, you cannot get the original password back), you can regain control of the switch after having lost or forgotten the encrypted password. See the “Recovering a Lost Enable Password” section for more information.

For information on how to display the password or access level configuration, see the “Displaying the Password, Access Level, and Privilege Level Configuration” section.

Configuring Multiple Privilege Levels

By default, Cisco IOS software has two modes of password security: user EXEC mode and privileged EXEC mode. 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 to more users. If you want more restricted access to the configure command, you can assign it level 3 security and distribute that password to fewer users.

The procedures in the following sections describe how to configure additional levels of security:

• Setting the Privilege Level for a Command
• Changing the Default Privilege Level for Lines
• Logging In to a Privilege Level
• Exiting a Privilege Level
• Displaying the Password, Access Level, and Privilege Level Configuration

Setting the Privilege Level for a Command

To set the privilege level for a command, perform this task:

For information on how to display the password or access level configuration, see the “Displaying the Password, Access Level, and Privilege Level Configuration” section.

Changing the Default Privilege Level for Lines

To change the default privilege level for a given line or a group of lines, perform this task:

For information on how to display the password or access level configuration, see the “Displaying the Password, Access Level, and Privilege Level Configuration” section.

Logging In to a Privilege Level

To log in at a specified privilege level, enter this command:

Exiting a Privilege Level

To exit to a specified privilege level, enter this command:

Displaying the Password, Access Level, and Privilege Level Configuration

To display detailed password information, perform this task:

This example shows how to display the password and access level configuration:

This example shows how to display the privilege level configuration:

Understanding the Supervisor Engine Boot Configuration

The supervisor engine boot process involves two software images: ROM monitor and supervisor engine software. When the switch is booted or reset, the ROMMON code is executed. Depending on the NVRAM configuration, the supervisor engine either stays in ROMMON mode or loads the supervisor engine software.

Two user-configurable parameters determine how the switch boots: the configuration register and the BOOT environment variable. The configuration register is described in the “Modifying the Boot Field and Using the boot Command” section. The BOOT environment variable is described in the “Specifying the Startup System Image” section.

Understanding the ROM Monitor

The ROM monitor (ROMMON) is invoked at switch bootup, reset, or when a fatal exception occurs. The switch enters ROMMON mode if the switch does not find a valid software image, if the NVRAM configuration is corrupted, or if the configuration register is set to enter ROMMON mode. From ROMMON mode, you can manually load a software image from bootflash or a flash disk, or you can boot up from the management interface. ROMMON mode loads a primary image from which you can configure a secondary image to boot up from a specified source either locally or through the network using the BOOTLDR environment variable. This variable is described in the “Switch#” section.

You can also enter ROMMON mode by restarting the switch and then pressing Ctrl-C during the first five seconds of startup. If you are connected through a terminal server, you can escape to the Telnet prompt and enter the send break command to enter ROMMON mode.

Note Ctrl-C is always enabled for five seconds after you reboot the switch, regardless of whether the configuration-register setting has Ctrl-C disabled.

The ROM monitor has these features:

• Power-on confidence test
• Hardware initialization
• Boot capability (manual bootup and autoboot)
• File system (read-only while in ROMMON)

Configuring the Software Configuration Register

The switch uses a 16-bit software configuration register, which allows you to set specific system parameters. Settings for the software configuration register are preconfigured in NVRAM.

Here are some reasons why you might want to change the software configuration register settings:

• To select a boot source and default boot filename
• To control broadcast addresses
• To set the console terminal baud rate
• To load operating software from flash memory
• To recover a lost password
• To manually boot the system using the boot command at the bootstrap program prompt
• To force an automatic bootup from the system bootstrap software (boot image) or from a default system image in onboard flash memory, and read any boot system commands that are stored in the configuration file in NVRAM

Caution To avoid possibly halting the switch, remember that valid configuration register settings might be combinations of settings and not just the individual settings listed in Table 3-3. For example, the factory default value of 0x2101 is a combination of settings.

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Table 3-3 lists the meaning of each of the software configuration memory bits. Table 3-4 defines the boot field.

Modifying the Boot Field and Using the boot Command

The configuration register boot field determines whether the switch loads an operating system image and, if so, where it obtains this system image. The following sections describe how to use and set the configuration register boot field and the procedures you must perform to modify the configuration register boot field. In ROMMON, to modify the configuration register and change boot settings, use the the confreg command.

Bits 0 through 3 of the software configuration register contain the boot field.

Note The factory default configuration register setting for systems and spares is 0x2101. However, the recommended value is 0x0102.

When the boot field is set to either 00 or 01 (0-0-0-0 or 0-0-0-1), the system ignores any boot instructions in the system configuration file and the following occurs:

• When the boot field is set to 00, you must boot up the operating system manually by entering the boot command at the system bootstrap or ROMMON prompt.
• When the boot field is set to 01, the system boots the first image in the bootflash single in-line memory module (SIMM).
• When the entire boot field equals a value between 0-0-1-0 and 1-1-1-1, the switch loads the system image specified by boot system commands in the startup configuration file.

Caution If you set bootfield to a value between 0-0-1-0 and 1-1-1-1, you must specify a value in the boot system command, else the switch cannot boot up and remains in ROMMON.

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You can enter the boot command only or enter the command and include additional boot instructions, such as the name of a file stored in flash memory, or a file that you specify for booting from a network server. If you use the boot command without specifying a file or any other boot instructions, the system boots from the default flash image (the first image in onboard flash memory). Otherwise, you can instruct the system to boot up from a specific flash image (using the boot system flash filename command).

You can also use the boot command to boot up images stored in the compact flash cards located in slot 0 on the supervisor engine.

Modifying the Boot Field

Modify the boot field from the software configuration register. To modify the software configuration register boot field, perform this task:

To modify the configuration register while the switch is running Cisco IOS software, follow these steps:

Step 1 Enter the enable command and your password to enter privileged level, as follows:

Step 2 Enter the configure terminal command at the EXEC mode prompt (#), as follows:

Step 3 Configure the configuration register to 0x102 as follows:

Set the contents of the configuration register by specifying the value command variable, where value is a hexadecimal number preceded by 0x (see Table 3-3).

Step 4 Enter the end command to exit configuration mode. The new value settings are saved to memory; however, the new settings do not take effect until the system is rebooted.

Step 5 Enter the show version EXEC command to display the configuration register value currently in effect; it is be used at the next reload. The value is displayed on the last line of the screen display, as shown in this sample output:

Step 6 Save your settings.

See the “Saving the Running Configuration Settings to Your Start-Up File” section. Note that configuration register changes take effect only after the system reloads, such as when you enter a reload command from the console.

Step 7 Reboot the system. The new configuration register value takes effect with the next system boot up.

Verifying the Configuration Register Setting

Enter the show version EXEC command to verify the current configuration register setting. In ROMMON mode, enter the show version command to verify the configuration register setting.

To verify the configuration register setting for the switch, perform this task:

In this example, the show version command indicates that the current configuration register is set so that the switch does not automatically load an operating system image. Instead, it enters ROMMON mode and waits for you to enter ROM monitor commands.

Supervisor Engine 6-E and Supervisor Engine 6L-E

Supervisor Engine 7-E, Supervisor Engine 7L-E, and Supervisor Engine 8-E

Specifying the Startup System Image

You can enter multiple boot commands in the startup configuration file or in the BOOT environment variable to provide backup methods for loading a system image.

The BOOT environment variable is also described in the “Specify the Startup System Image in the Configuration File” section in the “Loading and Maintaining System Images and Microcode” chapter of the Cisco IOS Configuration Fundamentals Configuration Guide.

Use the following sections to configure your switch to boot from flash memory. Flash memory can be either single in-line memory modules (SIMMs) or flash disks. Check the appropriate hardware installation and maintenance guide for information about types of flash memory.

Flash Memory Features

Flash memory allows you to do the following:

• Remotely load multiple system software images through TFTP or RCP transfers (one transfer for each file loaded)
• Boot a switch manually or automatically from a system software image stored in flash memory (you can also boot directly from ROM)
• Copy the system image to flash memory using TFTP
• Boot the system from flash memory either automatically or manually
• Copy the flash memory image to a network server using TFTP or RCP

For more information on flash memory, see this URL:

http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/hardware/configuration/notes/OL_2788.html

Security Precautions

Note the following security precaution when loading from flash memory:

Caution You can only change the system image stored in flash memory from privileged EXEC level on the console terminal.

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Configuring Flash Memory

To configure your switch to boot from flash memory, perform the following procedure. Refer to the appropriate hardware installation and maintenance publication for complete instructions on installing the hardware.

Step 1 Copy a system image to flash memory using TFTP, FTP, or through a VRF interface

Refer to section “Copy Configuration Files from a Network Server to the Router” in chapter “Managing Configuration Files”, of the “Managing Configuration Files Configuration Guide” at the following URL:

http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/config-mgmt/configuration/xe-3e/config-mgmt-xe-3e-book/cm-config-files.html.

Configure the system to boot automatically from the desired file in flash memory.

You might need to change the configuration register value. See the “Modifying the Boot Field and Using the boot Command” section, for more information on modifying the configuration register.

Step 2 Save your configurations.

Step 3 Power cycle and reboot your system to verify that all is working as expected.

Controlling Environment Variables

Although the ROM monitor controls environment variables, you can create, modify, or view them with certain commands. To create or modify the BOOT and BOOTLDR variables, use the boot system and boot bootldr global configuration commands, respectively. Refer to the “Specify the Startup System Image in the Configuration File” section in the “Loading and Maintaining System Images and Microcode” chapter of the Configuration Fundamentals Configuration Guide for details on setting the BOOT environment variable.

Note When you use the boot system and boot bootldr global configuration commands, you affect only the running configuration. To save the configuration for future use, you must save the environment variable settings to your startup configuration, which places the information under ROM monitor control. Enter the copy system:running-config nvram:startup-config command to save the environment variables from your running configuration to your startup configuration.

You can view the contents of the BOOT and BOOTLDR variables using the show bootvar command. This command displays the settings for these variables as they exist in the startup configuration and in the running configuration if a running configuration setting differs from a startup configuration setting. This example shows how to check the BOOT and BOOTLDR variables on the switch: