The RADIUS distributed client/server system allows you to secure networks against unauthorized access. In the Cisco implementation, RADIUS clients run on Cisco NX-OS devices and send authentication and accounting requests to a central RADIUS server that contains all user authentication and network service access information.
RADIUS can be implemented in a variety of network environments that require high levels of security while maintaining network access for remote users.
You can use RADIUS in the following network environments that require access security:
Networks with multiple-vendor network devices, each supporting RADIUS. For example, network devices from several vendors can use a single RADIUS server-based security database.
Networks already using RADIUS. You can add a Cisco NX-OS device with RADIUS to the network. This action might be the first step when you make a transition to a AAA server.
Networks that require resource accounting. You can use RADIUS accounting independent of RADIUS authentication or authorization. The RADIUS accounting functions allow data to be sent at the start and end of services, indicating the amount of resources (such as time, packets, bytes, and so on) used during the session. An Internet service provider (ISP) might use a freeware-based version of the RADIUS access control and accounting software to meet special security and billing needs.
Networks that support authentication profiles. Using the RADIUS server in your network, you can configure AAA authentication and set up per-user profiles. Per-user profiles enable the NX-OS device to better manage ports using their existing RADIUS solutions and to efficiently manage shared resources to offer different service-level agreements.
RADIUS Operation
When a user attempts to log in and authenticate to an NX-OS device using RADIUS, the following happens:
The user is prompted for and enters a username and password.
The username and encrypted password are sent over the network to the RADIUS server.
The user receives one of the following responses from the RADIUS server:
ACCEPT—The user is authenticated.
REJECT—The user is not authenticated and is prompted to reenter the username and password, or access is denied.
CHALLENGE—A challenge is issued by the RADIUS server. The challenge collects additional data from the user.
CHANGE PASSWORD—A request is issued by the RADIUS server, asking the user to select a new password.
The ACCEPT or REJECT response is bundled with additional data that is used for EXEC or network authorization. You must first complete RADIUS authentication before using RADIUS authorization. The additional data included with the ACCEPT or REJECT packets consists of the following:
Services that the user can access, including Telnet, rlogin, or local-area transport (LAT) connections, and Point-to-Point Protocol (PPP), Serial Line Internet Protocol (SLIP), or EXEC services.
Connection parameters, including the host or client IPv4 address, access list, and user timeouts.
RADIUS Server Monitoring
An unresponsive RADIUS server can cause a delay in processing AAA requests. You can periodically monitor a RADIUS server to check whether it is responding (or alive) to save time in processing AAA requests. Unresponsive RADIUS servers are marked as dead and are not sent AAA requests. Dead RADIUS servers are periodically monitored and returned to the alive state once they respond. This monitoring process verifies that a RADIUS server is in a working state before real AAA requests are sent its way. Whenever a RADIUS server changes to the dead or alive state, a Simple Network Management Protocol (SNMP) trap is generated and an error message is displayed indicating that a failure is taking place
Note
The monitoring interval for alive servers and dead servers are different and can be configured by the user. The RADIUS server monitoring is performed by sending a test authentication request to the RADIUS server.
Figure 1. Radius Server States
Vendor-Specific Attributes
The Internet Engineering Task Force (IETF) draft standard specifies a method for communicating vendor-specific attributes (VSAs) between the network access server and the RADIUS server. The IETF uses attribute 26. VSAs allow vendors to support their own extended attributes that are not suitable for general use. The Cisco RADIUS implementation supports one vendor-specific option using the format recommended in the specification. The Cisco vendor ID is 9, and the supported option is vendor type 1, which is named cisco-av-pair. The value is a string with the following format:
protocol : attribute separator value *
The protocol is a Cisco attribute for a particular type of authorization, the separator is = (equal sign) for mandatory attributes, and * (asterisk) indicates optional attributes.
When you use RADIUS servers for authentication, the RADIUS protocol directs the RADIUS server to return user attributes, such as authorization information, with authentication results. This authorization information is specified through VSAs.
The following VSA protocol options are supported:
Shell—Protocol used in access-accept packets to provide user profile information.
Accounting—Protocol used in accounting-request packets. If a value contains any white spaces, you should enclose the value within double quotation marks.
The following attributes are supported :
roles—Lists all the roles to which the user belongs. The value field is a string that lists the role names delimited by white space. For example, if the user belongs to roles network-operator and vdc-admin, the value field would be “network-operator vdc-admin.” This attribute, which the RADIUS server sends in the VSA portion of the Access-Accept frames, can only be used with the shell protocol value. The following examples show the roles attribute as supported by Cisco Access Control System ( ACS):
If you are using Cisco ACS and intend to use the same ACS group for both Cisco Nexus 1000V and Cisco UCS authentication, use the following roles attribute:
cisco-av-pair*shell:roles="network-admin admin"
Note
When you specify a VSA as shell:roles*"network-operator vdc-admin" or "shell:roles*\"network-operator vdc-admin\"", this VSA is flagged as an optional attribute and other Cisco devices ignore this attribute.
accountinginfo—Stores accounting information in addition to the attributes covered by a standard RADIUS accounting protocol. This attribute is sent only in the VSA portion of the Account-Request frames from the RADIUS client on the switch. It can be used only with the accounting protocol data units (PDUs).
Prerequisites for RADIUS
You already know the RADIUS server IP addresses or hostnames.
You already know the key(s) used to secure RADIUS communication in your network.
The device is already configured as a RADIUS client of the AAA servers.
Guidelines and Limitations
You can configure a maximum of 64 RADIUS servers.
Default Settings
Table 1 Default RADIUS Parameters
Parameters
Default
Server roles
Authentication and accounting
Dead timer interval
0 minutes
Retransmission count
1
Retransmission timer interval
5 seconds
Idle timer interval
0 minutes
Periodic server monitoring username
test
Periodic server monitoring password
test
Configuring RADIUS Servers
Configuring RADIUS Server Hosts
Use this procedure to configure the IP address or the hostname for each RADIUS server to be used for authentication. You should know the following information:
You can configure up to 64 RADIUS servers.
All RADIUS server hosts are automatically added to the default RADIUS server group.
Before You Begin
Before beginning this procedure, you must be logged in to the CLI in EXEC mode.
Specifies a preshared key for all RADIUS servers. You can specify a clear text (0) or encrypted (7) preshared key. The default format is clear text. The maximum length is 63 characters.
By default, no preshared key is configured.
Step 3
switch(config)# exit
Returns you to the EXEC mode.
Step 4
switch# show radius-server
(Optional)
Displays the RADIUS server configuration.
Note
The preshared keys are saved in encrypted form in the running configuration. Use the show running-config command to display the encrypted preshared keys.
Step 5
switch# copy running-config startup-config
(Optional)
Copies the running configuration to the startup configuration.
Specifies a preshared key for a specific RADIUS server. You can specify a clear text (0) or encrypted (7) preshared key. The default format is clear text. The maximum length is 63 characters.
Step 3
switch(config)# exit
Returns you to the EXEC mode.
Step 4
switch# show radius-server
(Optional)
Displays the RADIUS server configuration.
Note
The preshared keys are saved in encrypted form in the running configuration. Use the show running-config command to display the encrypted preshared keys.
Step 5
switch# copy running-config startup-config
(Optional)
Copies the running configuration to the startup configuration.
Use this procedure to configure a RADIUS server group whose member servers share authentication functions.
The servers in the group are tried in the same order in which you configure them
Before You Begin
Before beginning this procedure, you must be logged in to the CLI in EXEC mode.
All servers in a RADIUS server group must belong to the RADIUS protocol.
Procedure
Command or Action
Purpose
Step 1
switch# configure terminal
Enters global configuration mode.
Step 2
switch(config)# aaa group server radius group-name
Creates a RADIUS server group and enters the RADIUS server group configuration mode for that group. The group-name argument is a case-sensitive alphanumeric string with a maximum length of 127 characters.
Step 3
switch(config-radius)# server {ipv4-address | server-name}
Configures the RADIUS server as a member of the RADIUS server group.
Tip
If the specified RADIUS server is not found, configure it using the radius-server host command and retry this command.
Step 4
switch(config-radius)# deadtime minutes
(Optional)
Configures the monitoring dead time. The default is 0 minutes. The range is from 1 through 1440.
Note
If the dead-time interval for a RADIUS server group is greater than zero (0), that value takes precedence over the global dead-time value.
Step 5
switch(config-radius)# use-vrf vrf-name
(Optional)
Specifies the VRF to use to contact the servers in the server group
Copies the running configuration to the startup configuration
switch# configure terminal
switch(config)# aaa group server radius RadServer
switch(config-radius)# server 10.10.1.1
switch(config-radius)# deadtime 30
switch(config-radius)# use-vrf vrf1
switch(config-radius)# source-interface mgmt0
switch(config-radius)# show radius-server group
total number of groups:2
following RADIUS server groups are configured:
group Radserver:
server: 10.10.1.1
deadtime is 30
group test:
deadtime is 30
switch(config-radius)# copy running-config startup-config
Enabling RADIUS Server Directed Requests
You can allow users to designate the RADIUS server to send their authentication request to. This is called a directed request.
If you enable this option, a user can log in as username@vrfname:hostname, where vrfname is the virtual routing and forwarding (VRF) to use and hostname is the name of a configured RADIUS server.
Directed requests are disabled by default.
Note
User-specified logins are supported only for Telnet sessions.
Before You Begin
Before beginning this procedure, you must be logged in to the CLI in EXEC mode.
Procedure
Command or Action
Purpose
Step 1
switch# configure terminal
Enters global configuration mode.
Step 2
switch(config)# radius-server directed-request
Enables directed requests. The default is disabled.
Step 3
switch(config)# exit
Returns you to the EXEC mode.
Step 4
switch(config)# show radius-server directed-request
Use this procedure to configure the global timeout interval that specifies how long to wait for a response from a RADIUS server before declaring a timeout failure.
The timeout specified in the “Setting the Timeout Interval for a Single RADIUS Server” section overrides the global RADIUS timeout.
Before You Begin
Before beginning this procedure, you must be logged in to the CLI in EXEC mode.
Procedure
Command or Action
Purpose
Step 1
switch# configure terminal
Places you into global configuration mode.
Step 2
switch(config)# radius-server timeout seconds
Specifies the transmission timeout interval for RADIUS servers. The default timeout interval is 5 seconds and the allowable range is from 1 to 60 seconds.
Configuring a Global Retry Count for All RADIUS Servers
Use this procedure to configure the maximum number of times to retry transmitting to a RADIUS server before reverting to local authentication.This setting is applied to all RADIUS servers.
By default, retransmission to a RADIUS server is only tried once before reverting to local authentication.
You can increase the number of retries up to a maximum of five.
The retry count specified for a single RADIUS server in the “Configuring Retries for a Single RADIUS Server” section, overrides this global setting.
Before You Begin
Before beginning this procedure, you must be logged in to the CLI in EXEC mode.
Procedure
Command or Action
Purpose
Step 1
switch# configure terminal
Places you into global configuration mode.
Step 2
switch(config)# radius-server retransmitcount
Defines the number of retransmits allowed before reverting to local authentication. This global setting applies to all RADIUS servers. The default number of retransmits is 1 and the range is from 0 to 5.
Step 3
switch(config)# exit
Returns you to the EXEC mode.
Step 4
switch# show radius-server
(Optional)
Displays the RADIUS server configuration
Step 5
switch# copy running-config startup-config
(Optional)
Copies the running configuration to the startup configuration.
Use this procedure to configure the maximum number of times to retry transmitting to a RADIUS server before reverting to local authentication.This setting applies to a single RADIUS server and takes precedence over the global retry count.
Before You Begin
Before beginning this procedure, you must be logged in to the CLI in EXEC mode.
You should know the following:
By default, retransmission to a RADIUS server is only tried once before reverting to local authentication.
You can increase the number of retries up to a maximum of five.
The retry count specified for a single RADIUS server overrides the global setting made for all RADIUS servers.
Use this procedure to configure the monitoring of RADIUS servers.
The test idle timer specifies the interval of time that elapses before a test packet is sent to a non-responsive RADIUS server
The default idle timer value is 0 minutes. When the idle time interval is 0 minutes, the Cisco NX-OS device does not perform periodic RADIUS server monitoring.
Note
For security reasons, do not configure a username that is in the RADIUS database as a test username.
Before You Begin
Before beginning this procedure, you must be logged in to the CLI in EXEC mode.
Specifies parameters for server monitoring. The default username is test and the default password is test. The default value for the idle timer is 0 minutes. The valid range is from 0 to 1440 minutes.
Note
For periodic RADIUS server monitoring, you must set the idle timer to a value greater than 0.
Step 3
switch(config)# radius-server dead-timeminutes
Specifies the number of minutes to wait before sending a test packet to a RADIUS server that was declared dead. The default value is 0 minutes. The valid range is 1 to 1440 minutes.
Step 4
switch(config)# exit
Returns you to the EXEC mode.
Step 5
switch# show radius-server
(Optional)
Displays the RADIUS server configuration
Step 6
switch# copy running-config startup-config
(Optional)
Copies the running configuration to the startup configuration.
Use this procedure to configure the dead-time interval for all RADIUS servers. The dead-time interval specifies the time to wait after declaring a RADIUS server dead, before sending out a test packet to determine if the server is now alive. The default value is 0 minutes
Note
When the dead-time interval is 0 minutes, RADIUS servers are not marked as dead even if they are not responding. You can configure the dead-time interval for a RADIUS server group.
Before You Begin
Before beginning this procedure, you must be logged in to the CLI in EXEC mode.
Procedure
Command or Action
Purpose
Step 1
switch# configure terminal
Enters global configuration mode.
Step 2
switch(config)# radius-server deadtime minutes
Configures the dead-time interval. The default value is 0 minutes. The range is from 1 to 1440 minutes.
Step 3
switch(config)# exit
Returns you to the EXEC mode.
Step 4
switch# show radius-server
(Optional)
Displays the RADIUS server configuration.
Step 5
switch# copy running-config startup-config
(Optional)
Copies the running configuration to the startup configuration.