Cisco IOS Configuration Guide for Autonomous Cisco Aironet Access Points - Release 15.3(3)JBB

Understanding RADIUS

RADIUS is a distributed client/server system that secures networks against unauthorized access. RADIUS clients run on supported Cisco devices and send authentication requests to a central RADIUS server, which contains all user authentication and network service access information. The RADIUS host is normally a multiuser system running RADIUS server software from Cisco (Cisco Identity Services Engine), FreeRADIUS, Microsoft, or another software provider. For more information, refer to the RADIUS server documentation.

Use RADIUS in these network environments, which require access security:

• Networks with multiple-vendor access servers, each supporting RADIUS. For example, access servers from several vendors use a single RADIUS server-based security database. In an IP-based network with multiple vendors’ access servers, dial-in users are authenticated through a RADIUS server that is customized to work with the Kerberos security system.
• Turnkey network security environments in which applications support the RADIUS protocol, such as an access environment that uses a smart card access control system.
• Networks already using RADIUS. You can add a Cisco access point containing a RADIUS client to the network.
• Networks that require resource accounting. You can use RADIUS accounting independently of RADIUS authentication or authorization. The RADIUS accounting functions allow data to be sent at the start and end of services, showing the amount of resources (such as time, packets, bytes, and so forth) used during the session. An Internet service provider might use a freeware-based version of RADIUS access control and accounting software to meet special security and billing needs.

RADIUS is not suitable in these network security situations:

• Multiprotocol access environments– RADIUS does not support, for example, AppleTalk Remote Access (ARA), NetBIOS Frame Control Protocol (NBFCP), NetWare Asynchronous Services Interface (NASI), or X.25 PAD connections.
• Networks using a variety of services. RADIUS generally binds a user to one service model.

RADIUS Operation

When a wireless user attempts to log in and authenticate to an access point whose access is controlled by a RADIUS server, authentication to the network occurs in the steps shown in Figure 13-1:

Figure 13-1 Sequence for EAP Authentication

As shown in Figure 13-1, at the start, a wireless client device and a RADIUS server on the wired LAN use 802.1x and EAP to perform a mutual authentication through the access point. The initial phase is an 802.11 open authentication and association. The EAP process then starts.

The AP communicates with the client over the wireless link using EAP/802.1x, and relays the client messages to the RADIUS server using RADIUS encapsulation. Once the client and the authentication server agrees on an EAP method, the RADIUS server sends an authentication challenge to the client.

Some EAP methods also require the client to authenticate the RADIUS server before accepting a challenge from the server. In all cases, the credential exchange is encrypted and cannot be read by eavesdroppers.

When (one way or mutual) authentication is complete, and when WPA/WPA2 is in use, the RADIUS server and the client derive an initial key called Pairwise Master Key (PMK). The the client and the RADIUS server use the same method to derive the PKM, and therefore derive the same PMK. However, the PMK is not exchanged over the wireless link.

The RADIUS server sends a copy of the PMK to the AP. The AP and the client will then use this PMK to derive unicast encryption keys that will be used to encrypt the exchanges between the client and the AP during the client session. The AP will also use the unicast encryption key to communicate to the client the broadcast key, or the key used to encrypt traffic broadcasted to all clients in the cell.

There is more than one type of EAP authentication, but the access point behaves the same way for each type. The AP relays authentication messages from the wireless client device to the RADIUS server and from the RADIUS server to the wireless client device. See the “Assigning Authentication Types to an SSID” for instructions on setting up client authentication using a RADIUS server.

Configuring RADIUS

This section describes how to configure your access point to support RADIUS. At the minimum, you must identify the host(s) that run the RADIUS server software and define the method lists for RADIUS authentication. You can optionally define method lists for RADIUS 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.

You should have access to and should configure a RADIUS server before configuring RADIUS features on your access point.

This section contains this configuration information:

• Default RADIUS Configuration
• Identifying the RADIUS Server Host (required)
• Configuring RADIUS Login Authentication (required)
• Defining AAA Server Groups (optional)
• Configuring RADIUS Authorization for User Privileged Access and Network Services (optional)
• Configuring Packet of Disconnect (optional)
• Starting RADIUS Accounting (optional)
• Configuring Settings for All RADIUS Servers (optional)
• Configuring Settings for All RADIUS Servers (optional)
• Configuring the Access Point to Use Vendor-Specific RADIUS Attributes (optional)
• Configuring the Access Point for Vendor-Proprietary RADIUS Server Communication (optional)
• Configuring WISPr RADIUS Attributes (optional)

Note The RADIUS server CLI commands are disabled until you enter the aaa new-model command.

Default RADIUS Configuration

RADIUS and AAA are disabled by default.

To prevent a lapse in security, you cannot configure RADIUS through a network management application. When enabled, RADIUS can authenticate users accessing the access point through the CLI.

Identifying the RADIUS Server Host

Access point-to-RADIUS-server communication involves several components:

• Host name or IP address
• Authentication destination port
• Accounting destination port
• Key string
• Timeout period
• Retransmission value

You identify RADIUS security servers by their host name or IP address, host name and specific UDP port numbers, or their IP address and specific UDP port numbers. The combination of the IP address and the UDP port number creates a unique identifier allowing different ports to be individually defined as RADIUS hosts providing a specific AAA service. This unique identifier enables RADIUS requests to be sent to multiple UDP ports on a server at the same IP address.

Note For Cisco IOS Releases 12.2(8)JA and later, the access point uses a randomly chosen UDP source port number in the range of 21645 to 21844 for communication with RADIUS servers.

If two different host entries on the same RADIUS server are configured for the same service—such as accounting—the second host entry configured acts as a fail-over backup to the first one. Using this example, if the first host entry fails to provide accounting services, the access point tries the second host entry configured on the same device for accounting services. (The RADIUS host entries are tried in the order that they are configured.)

A RADIUS server and the access point use a shared secret text string to encrypt passwords and exchange responses. To configure RADIUS to use the AAA security commands, you must specify the host running the RADIUS server daemon and a secret text (key) string that it shares with the access point.

The timeout, retransmission, and encryption key values can be configured globally per server for all RADIUS servers or in some combination of global and per-server settings. To apply these settings globally to all RADIUS servers communicating with the access point, use the three unique global configuration commands: radius-server timeout, radius-server retransmit, and radius-server key. To apply these values on a specific RADIUS server, use the radius-server host global configuration command.

Note If you configure both global and per-server functions (timeout, retransmission, and key commands) on the access point, the per-server timer, retransmission, and key value commands override global timer, retransmission, and key value commands. For information on configuring these setting on all RADIUS servers, see the “Configuring Settings for All RADIUS Servers” section.

You can configure the access point to use AAA server groups to group existing server hosts for authentication. For more information, see the “Defining AAA Server Groups” section.

Beginning in privileged EXEC mode, follow these steps to configure per-server RADIUS server communication. This procedure is required.

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	aaa new-model	Enable AAA.
Step 3	radius-server {hostname | ip-address}[ auth-port port-number ] [ acct-port port-number ] [ timeout seconds ] [ retransmit retries ] [ key string ] Note This command was supported in the older releases. You are recommended to use the following new commands. radius server name address [ IP address ip-address ] [ auth-port port-number ] [ acct-port port-number ] address {ipv4 radius-server-IPv4-Address | ipv6 radius-server-IPv6-Address}	Specify the server name of the remote RADIUS server host. (Optional) For auth-port port-number, specify the UDP destination port for authentication requests.(Optional) For acct-port port-number, specify the UDP destination port for accounting requests. (Optional) For timeout seconds, specify the time interval that the access point waits for the RADIUS server to reply before retransmitting. The range is 1 to 1000. This setting overrides the radius-server timeout global configuration command setting. If no timeout is set with the radius-server host command, the setting of the radius-server timeout command is used. (Optional) For retransmit retries, specify the number of times a RADIUS request is resent to a server if that server is not responding or responding slowly. The range is 1 to 1000. If no retransmit value is set with the radius-server host command, the setting of the radius-server retransmit global configuration command is used. (Optional) For key string, specify the authentication and encryption key used between the access point and the RADIUS daemon running on the RADIUS server. Note The key is a text string that must match the encryption key used on the RADIUS server. Always configure the key as the last item in the radius-server host command. Leading spaces are ignored, but spaces within and at the end of the key are used. If you use spaces in your key, do not enclose the key in quotation marks unless the quotation marks are part of the key. To configure the access point to recognize more than one host entry associated with a single IP address, enter this command as many times as necessary, making sure that each UDP port number is different. The access point software searches for hosts in the order in which you specify them. Set the timeout, retransmit, and encryption key values to use with the specific RADIUS host.
Step 4	dot11 ssid ssid-string	Enter SSID configuration mode for an SSID on which you need to enable accounting. The SSID can consist of up to 32 alphanumeric characters. SSIDs are case sensitive.
Step 5	accounting list-name	Enable RADIUS accounting for this SSID. For list-name, specify the accounting method list. Click this URL for more information on method lists: http://www.cisco.com/c/en/us/td/docs/ios/12_2/security/configuration/guide/fsecur_c/scfacct.html Note To enable accounting for an SSID, you must include the accounting command in the SSID configuration. Click this URL to browse to a detailed description of the SSID configuration mode accounting 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 remove the specified RADIUS server, use the no radius-server host hostname | ip-address global configuration command.

This example shows how to configure one RADIUS server to be used for authentication and another to be used for accounting:

This example shows how to configure an SSID for RADIUS accounting:

This example shows how to configure host1 as the RADIUS server and to use the default ports for both authentication and accounting:

Note You also need to configure some settings on the RADIUS server. These settings include the IP address of the access point and the key string to be shared by both the server and the access point. For more information, refer to the RADIUS server documentation.

Configuring RADIUS 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 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. This procedure is required.

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 RADIUS authentication for logins or to return to the default value, use the no login authentication { default | list-name } line configuration command.

Defining AAA Server Groups

You can configure the access point to use AAA server groups to group existing server hosts for authentication. You 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, which lists the IP addresses of the selected server hosts.

Server groups also can include multiple host entries for the same server if each entry has a unique identifier (the combination of the IP address and UDP port number), allowing different ports to be individually defined as RADIUS hosts providing a specific AAA service. If you configure two different host entries on the same RADIUS server for the same service (such as accounting), the second configured host entry acts as a fail-over backup to the first one.

You use the server group server configuration command to associate a particular server with a defined group server. You can either identify the server by its IP address or identify multiple host instances or entries by using the optional auth-port and acct-port keywords.

Beginning in privileged EXEC mode, follow these steps to define the AAA server group and associate a particular RADIUS server with it:

To remove the specified RADIUS server, use the no radius-server host hostname | ip-address global configuration command. To remove a server group from the configuration list, use the no aaa group server radius group-name global configuration command. To remove the IP address of a RADIUS server, use the no server ip-address server group configuration command.

In this example, the access point is configured to recognize two different RADIUS group servers ( group1 and group2). Group1 has two different host entries on the same RADIUS server configured for the same services. The second host entry acts as a fail-over backup to the first entry.

Note The ports defined for each RADIUS server host in a radius group override the ports defined individually for each radius server host entry created from global configuration mode.

Configuring RADIUS Authorization for User Privileged Access and Network Services

AAA authorization limits the services available to a user. When AAA authorization is enabled, the access point uses information retrieved from the user’s profile, which is 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.

Note This section describes setting up authorization for access point administrators, not for wireless client devices. For wireless client devices and wireless network access authorization, no specific authorization profile needs to be returned from the RADIUS server.

You can use the aaa authorization global configuration command with the radius keyword to set parameters that restrict a user’s network access to privileged EXEC mode.

The aaa authorization exec radius local command sets these authorization parameters:

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

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

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

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

Configuring Packet of Disconnect

Packet of Disconnect (PoD) is also known as Disconnect Message. Additional information on PoD can be found in the Internet Engineering Task Force (IETF) Internet Standard RFC 3576

Packet of Disconnect consists of a method of terminating a session that has already been connected. The PoD is a RADIUS Disconnect_Request packet and is intended to be used in situations where the authenticating agent server wants to disconnect the user after the session has been accepted by the RADIUS access_accept packet.

When a session is terminated, the RADIUS server sends a disconnect message to the Network Access Server (NAS); an access point or WDS. For 802.11 sessions, the Calling-Station-ID [31] RADIUS attribute (the MAC address of the client) must be supplied in the Pod request. The access point or WDS attempts to disassociate the relevant session and then sends a disconnect response message back to the RADIUS server. The message types are as follows:

• 40—Disconnect-Request
• 41—Disconnect—ACK
• 42—Disconnect—NAK

Note Refer to your RADIUS server application documentation for instructions on how to configure PoD requests.

Note The access point does not block subsequent attempts by the client to reassociate. It is the responsibility of the security administrator to disable the client account before issuing a PoD request.

Note When WDS is configured, PoD requests should be directed to the WDS. The WDS forwards the disassociation request to the parent access point and then purges the session from its own internal tables.

Beginning in privileged EXEC mode, follow these steps to configure a PoD:

Selecting the CSID Format

You can select the format for MAC addresses in Called-Station-ID (CSID) and Calling-Station-ID attributes in RADIUS packets.

The Calling-Station-ID [31] RADIUS attribute is the MAC address of the wireless client, and may need to be communicated to the RADIUS server, for example, for accounting or for the PoD.

Use the dot11 aaa csid global configuration command to select the CSID format. Table 13-1 lists the format options with corresponding MAC address examples.

To return to the default CSID format, use the no form of the dot11 aaa csid command, or enter
dot11 aaa csid default.

Note You can also use the wlccp wds aaa csid command to select the CSID format.

Starting RADIUS 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 access point reports user activity to the RADIUS 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. See the “RADIUS Attributes Sent by the Access Point” section for a complete list of attributes sent and honored by the access point.

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

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

Configuring Settings for All RADIUS Servers

Beginning in privileged EXEC mode, follow these steps to configure global communication settings between the access point and all RADIUS servers:

This example shows how to set up two main servers with a server deadtime of 10 minutes:

To return to the default setting for retransmit, timeout, and deadtime, use the no forms of these commands.

Configuring the Access Point to Use Vendor-Specific RADIUS Attributes

Note The following configuration is done on the RADIUS server.

The Internet Engineering Task Force (IETF) draft standard specifies a method for communicating vendor-specific information between the access point and the RADIUS server by using the vendor-specific attribute (attribute 26). Vendor-specific attributes (VSAs) allow vendors to support their own extended attributes not suitable for general use. The Cisco RADIUS implementation supports one vendor-specific option by using the format recommended in the specification. Cisco’s vendor ID is 9, and the supported option has vendor type 1, which is named cisco-avpair. The value is a string with this format:

Protocol is a value of the Cisco protocol attribute for a particular type of authorization. Attribute and value are an appropriate AV pair defined in the Cisco TACACS+ specification, and sep is = for mandatory attributes and the asterisk ( *) for optional attributes. This allows the full set of features available for TACACS+ authorization to also be used for RADIUS.

For example, the following AV pair activates Cisco’s multiple named ip address pools feature during IP authorization (during PPP’s IPCP address assignment):

The following example shows how to provide a user logging in from an access point with immediate access to privileged EXEC commands:

Other vendors have their own unique vendor IDs, options, and associated VSAs. For more information about vendor IDs and VSAs, refer to RFC 2138, “Remote Authentication Dial-In User Service (RADIUS).”

Beginning in privileged EXEC mode, follow these steps to configure the access point to recognize and use VSAs:

For a complete list of RADIUS attributes or more information about VSA 26, see the RADIUS guides at the following URL:
http://www.cisco.com/en/US/docs/ios-xml/ios/security/config_library/12-4t/secuser-12-4t-library.html

Configuring the Access Point for Vendor-Proprietary RADIUS Server Communication

Although an IETF draft standard for RADIUS specifies a method for communicating vendor-proprietary information between the access point and the RADIUS server, some vendors have extended the RADIUS attribute set in a unique way. Cisco IOS software supports a subset of vendor-proprietary RADIUS attributes.

As mentioned earlier, to configure RADIUS (whether vendor-proprietary or IETF draft-compliant), you must specify the host running the RADIUS server daemon and the secret text string it shares with the access point. You specify the RADIUS host and secret text string by using the radius-server global configuration commands.

Beginning in privileged EXEC mode, follow these steps to specify a vendor-proprietary RADIUS server host and a shared secret text string:

To delete the vendor-proprietary RADIUS host, use the no radius-server host {hostname | ip-address} non-standard global configuration command. To disable the key, use the no radius-server key global configuration command.

This example shows how to specify a vendor-proprietary RADIUS host and to use a secret key of rad124 between the access point and the server:

Configuring WISPr RADIUS Attributes

The Wi-Fi Alliance’s WISPr Best Current Practices for Wireless Internet Service Provider Roaming, and its updated Annex D published in 2010 by the Wireless Broadband Alliance under the name WISPv2 lists RADIUS attributes that access points must send with RADIUS accounting and authentication requests. The access point currently supports only the WISPr location-name and the ISO and International Telecommunications Union (ITU) country and area codes attributes. Use the snmp-server location and the dot11 location isocc commands to configure these attributes on the access point.

The WISPr and WISPv2 Best Current Practices for Wireless Internet Service Provider Roaming (WISPr) document also requires the access point to include a class attribute in RADIUS authentication replies and accounting requests. The access point includes the class attribute automatically and does not have to be configured to do so.

You can find a list of ISO and ITU country and area codes at the ISO and ITU websites. Cisco IOS software does not check the validity of the country and area codes that you configure on the access point.

Beginning in privileged EXEC mode, follow these steps to specify WISPr RADIUS attributes on the access point:

This example shows how to configure the WISPr location-name attribute:

This example shows how to configure the ISO and ITU location codes on the access point:

This example shows how the access point adds the SSID used by the client device and formats the location-ID string:

Displaying the RADIUS Configuration

To display the RADIUS configuration, use the show running-config p rivileged EXEC command.

Note When DNS is configured on the access point, the show running-config command sometimes displays a server’s IP address instead of its name.

RADIUS Attributes Sent by the Access Point

Table 13-2 through Table 13-6 identify the attributes sent by an access point to a client in access-request, access-accept, and accounting-request packets.

Note You can configure the access point to include in its RADIUS accounting and authentication requests attributes recommended by the Wi-Fi Alliance’s WISPr and WISPv2 Best Current Practices for Wireless Internet Service Provider Roaming (WISPr) document. Refer to the “Configuring WISPr RADIUS Attributes” section for instructions.

Note By default, the access point sends reauthentication requests to the authentication server with the service-type attribute set to authenticate-only. However, some Microsoft IAS servers do not support the authenticate-only service-type attribute. Depending on the user requirements, set the service-type attribute to: dot11 aaa authentication attributes service-type login-user or dot11 aaa authentication attributes service-type framed-user. By default the service type "login" is sent in the access request.

Understanding TACACS+

TACACS+ is a security application that provides centralized validation of users attempting to gain access to your access point. Unlike RADIUS, TACACS+ does not authenticate wireless client devices accessing the network through your access point.

You should have access to and should configure a TACACS+ server before configuring TACACS+ features on your access point.

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.

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

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

The authentication facility can conduct a dialog with the administrator (for example, 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 administrator screens. For example, a message could notify administrators that their passwords must be changed because of the company’s password aging policy.

• Authorization—Provides fine-grained control over administrator capabilities for the duration of the administrator’s session, including but not limited to setting autocommands, access control, session duration, or protocol support. You can also enforce restrictions on the commands that an administrator 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 administrator activity for a security audit or to provide information for user billing. Accounting records include administrator identities, start and stop times, executed commands, number of packets, and number of bytes.

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

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

TACACS+ Operation

When an administrator attempts a simple ASCII login by authenticating to an access point using TACACS+, this process occurs:

1. When the connection is established, the access point contacts the TACACS+ daemon to obtain a username prompt, which is then displayed to the administrator. The administrator enters a username, and the access point then contacts the TACACS+ daemon to obtain a password prompt. The access point displays the password prompt to the administrator, the administrator 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 administrator until the daemon receives enough information to authenticate the administrator. The daemon prompts for a username and password combination, but can include other items, such as e.g. the user mother maiden name, or any other information configured on the TACACS as being mandatory to identify the user.

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

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

– REJECT—The administrator is not authenticated. The administrator 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 access point. If an ERROR response is received, the access point typically tries to use an alternative method for authenticating the administrator.

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

After authentication, the administrator undergoes an additional authorization phase if authorization has been enabled on the access point. Administrators 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 administrator, determining the services that the administrator can access:

– Telnet, rlogin, or privileged EXEC services

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

Configuring TACACS+

This section describes how to configure your access point 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 an administrator. 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 administrators; 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 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 administrators accessing the access point through the CLI and the web interface.

Identifying the TACACS+ Server Host and Setting the Authentication Key

You can configure the access point 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:

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, 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 an administrator. 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 administrator access—the authentication process stops, and no other authentication methods are attempted.

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

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

You can use the aaa authorization global configuration command with the tacacs+ keyword to set parameters that restrict an administrator’s network access to privileged EXEC mode.

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 administrators who log in through the CLI even if authorization has been configured.

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

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

You also need to configure your TACACS server with user credentials, and also configure the TACACS server to return an authorization profile for the authenticated user. The profile can be as extensive as shell privilege level 15, with no restriction of commands; or be more specific and target only a set of commands or a lower privilege level.

Starting TACACS+ Accounting

The AAA accounting feature tracks the services that administrators are accessing and the amount of network resources that they are consuming. When AAA accounting is enabled, the access point reports administrator 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:

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.