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This chapter contains the following sections:
The TACACS+ security protocol provides centralized validation of users who are attempting to gain access to a device. TACACS+ services are maintained in a database on a TACACS+ daemon that is running, typically, on a UNIX or Windows NT workstation. You must have access to and must configure a TACACS+ server before the configured TACACS+ features on your device are available.
TACACS+ provides for separate authentication, authorization, and accounting services. The TACACS+ daemon provides each service independently. Each service can be tied into its own database to take advantage of other services available on that server or on the network, depending on the capabilities of the daemon.
The TACACS+ client/server protocol uses TCP (TCP port 49) for transport requirements. Centralized authentication is provided using the TACACS+ protocol.
The following sequence of events take place when you attempt to log in to a TACACS+ server using the Password Authentication Protocol (PAP):
Note |
TACACS+ allows an arbitrary conversation between the daemon and the user until the daemon receives enough information to authenticate the user. This action is usually done by prompting for a username and password combination, but might include prompts for additional information, such as your mother’s maiden name. |
You must configure the TACACS+ preshared key to authenticate to the TACACS+ server. A preshared key is a secret text string shared between the device and the TACACS+ server host. The length of the key is restricted to 63 characters and can include any printable ASCII characters (white spaces are not allowed). You can configure a global preshared secret key for all TACACS+ server configurations.
You can override the global preshared key assignment by explicitly using the key option when configuring an individual TACACS+ server.
Unresponsive TACACS+ servers are marked as dead and are not sent AAA requests. Dead TACACS+ servers are periodically monitored and brought back alive once they respond. This process confirms that a TACACS+ server is in a working state before real AAA requests are sent its way. The following figure shows how a TACACS+ server state change generates a Simple Network Management Protocol (SNMP) trap and an error message showing the failure before it impacts performance.
Note |
The monitoring interval for alive servers and dead servers are different and can be configured by the user. The TACACS+ server monitoring is performed by sending a test authentication request to the TACACS+ server. |
The Internet Engineering Task Force (IETF) draft standard specifies a method for communicating vendor-specific attributes (VSAs) between the network access server and the TACACS+ server. The IETF uses attribute 26. VSAs allow vendors to support their own extended attributes that are not suitable for general use.
The Cisco TACACS+ implementation supports one vendor-specific option using the format recommended in the IETF 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 TACACS+ servers for authentication, the TACACS+ protocol directs the TACACS+ 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:
The following attributes are other supported:
Parameters |
Default |
---|---|
TACACS+ |
Disabled |
Dead timer interval |
0 minutes |
Timeout interval |
5 seconds |
Idle timer interval |
0 minutes |
Periodic server monitoring username |
test |
Periodic server monitoring password |
test |
The following flowchart steps you through configuring TACACS+
Note |
Be aware that the Cisco Nexus 1000V commands might differ from the Cisco IOS commands. |
By default, TACACS+ is disabled. You must explicitly enable the TACACS+ feature to access the configuration and verification commands that support TACACS+ authentication.
Caution |
When you disable TACACS+, all related configurations are automatically discarded. |
Before beginning this procedure, you must be logged in to the CLI in EXEC mode.
switch# configure terminal switch(config)# tacacs+ enable switch(config)# exit switch# copy running-config startup-config
By default, no global key is configured.
Use this procedure to configure the following:
switch# configure terminal switch(config)# tacacs-server key 0 QsEFtkI# switch(config)# exit switch# show tacacs-server Global TACACS+ shared secret:******** timeout value:5 deadtime value:0 total number of servers:1 following TACACS+ servers are configured: 10.10.2.2: available on port:49 switch# copy running-config startup-config
All TACACS+ server hosts are added to the default TACACS+ server group.
Before beginning this procedure, you must have done the following:
Command or Action | Purpose | |
---|---|---|
Step 1 | switch# configure terminal | Places you into global configuration mode. |
Step 2 | switch(config)# tacacs-server host {ipv4-address | host-name} | Configures the server IP address or hostname as a TACACS+ server host. |
Step 3 | switch(config)# exit | Exits the global configuration mode and returns you to EXEC mode. |
Step 4 | switch(config)# show tacacs-server | (Optional) Displays the TACACS+ server configuration. |
Step 5 | switch(confgi)# copy running-config startup-config | (Optional) Copies the running configuration to the startup configuration |
switch# configure terminal switch(config)# tacacs-server host 10.10.2.2 switch(config)# exit switch# show tacacs-server timeout value:5 deadtime value:0 total number of servers:1 following TACACS+ servers are configured: 10.10.2.2: available on port:49 switch# copy running-config startup-config
Use this procedure to configure a TACACS+ server group whose member servers share authentication functions.
After you configure the TACACS+ server group, the server members are tried in the same order in which you configured them.
A TACACS+ server group can provide a failover if one server fails to respond. If the first server in the group fails, the next server in the group is tried until a server responds. Multiple server groups can provide failovers for each other in this same way.
Before beginning this procedure, you must be sure of the following:
Command or Action | Purpose | |||
---|---|---|---|---|
Step 1 | switch# configure terminalt | Places you into global configuration mode. |
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Step 2 | switch(config)# aaa group server tacacs+ group-name | Creates a TACACS+ server group with the specified name and places you into the TACACS+ configuration mode for that group. |
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Step 3 | switch(config-tacacs+)# server { ipv4-address | host-name} | Configures the TACACS+ server hostname or IP address as a member of the TACACS+ server group. If the specified TACACS+ server is not found, configure it using the tacacs-server host command and retry this command.
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Step 4 | switch(config-tacacs+)# deadtime minutes | (Optional) Configures the monitoring dead time for this TACACS+ group. The default is 0 minutes. The range is from 0 through 1440.
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Step 5 | switch(config-tacacs+)# use-vrf vrf-name | (Optional) Specifies the virtual routing and forwarding instance (VRF) to use to contact this server group |
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Step 6 | switch(config-tacacs+)# source-interface {interface-type} {interface-number} | (Optional) Specifies a source interface to be used to reach the TACACS+ server. |
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Step 7 | switch(config-tacacs+)# show tacacs-server groups | (Optional) Displays the TACACS+ server group configuration |
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Step 8 | switch(config-tacacs+)# copy running-config startup-config | (Optional) Copies the running configuration to the startup configuration. |
switch# config terminal switch(config)# aaa group server tacacs+ TacServer switch(config-tacacs+)# server 10.10.2.2 switch(config-tacacs+)# deadtime 30 switch(config-tacacs+)# use-vrf management switch(config-tacacs+)# source-interface mgmt0 switch(config-tacacs+)# show tacacs-server groups total number of groups:1 following TACACS+ server groups are configured: group TacServer: server 10.10.2.2 on port 49 deadtime is 30 vrf is management switch# copy running-config startup-config
This procedure allows you to designate the TACACS+ server to send their authentication request to. This is called a directed-request.
Note |
User-specified logins are only supported for Telnet sessions. |
Before beginning this procedure, be sure you have done the following:
Command or Action | Purpose | |
---|---|---|
Step 1 | switch# configure terminal | Places you into global configuration mode. |
Step 2 | switch(config)# tacacs-server directed-request | Enables use of directed requests for specifying the TACACS+ server to send an authentication request to when logging in. The default is disabled. |
Step 3 | switch(config)# exit | Exits the global configuration mode and returns you to EXEC mode. |
Step 4 | switch(config)# show tacacs-server directed-request | (Optional) Displays the TACACS+ directed request configuration. |
Step 5 | switch(config)# copy running-config startup-config | Copies the running configuration to the startup configuration |
switch# config terminal switch(config)# tacacs-server directed-request switch(config)# exit switch# show tacacs-server directed-request enabled switch# copy running-config startup-config
Use this procedure to set the interval in seconds that the Cisco Nexus 1000V waits for a response from any TACACS+ server before declaring a timeout.
The timeout specified for an individual TACACS+ server overrides the global timeout interval. To set the timeout for an individual server.
Before beginning this procedure, you must be sure you have done the following:
Command or Action | Purpose | |
---|---|---|
Step 1 | switch# configure terminal | Places you into global configuration mode. |
Step 2 | switch(config)# tacacs-server timeout seconds | Specifies the interval in seconds that the Cisco Nexus 1000V waits for a response from a server. The default timeout interval is 5 seconds. The range is from 1 to 60 seconds. |
Step 3 | switch(confi)# exit | Exits the global configuration mode and returns you to EXEC mode. |
Step 4 | switch(config)# show tacacs-server | (Optional) Displays the TACACS+ server configuration. |
Step 5 | switch(confi)# copy running-config startup-config | (Optional) Copies the running configuration to the startup configuration |
switch# configure terminal switch(config)# tacacs-server timeout 10 switch(config)# exit switch# n1000v# show tacacs-server Global TACACS+ shared secret:******** timeout value:10 deadtime value:0 total number of servers:1 following TACACS+ servers are configured: 10.10.2.2: available on port:49 switch# copy running-config startup-config
Use this procedure to set the interval in seconds that the Cisco Nexus 1000V waits for a response from a specific TACACS+ server before declaring a timeout. This setting is configured per TACACS+ host.
The timeout setting for an individual TACACS+ server overrides the global timeout interval.
Before beginning this procedure, you must be sure you have done the following:
Command or Action | Purpose | |
---|---|---|
Step 1 | switch# configure terminal | Places you into global configuration mode. |
Step 2 | switch(config)# tacacs-server host {ipv4-address | host-name} timeout seconds | Specifies the timeout interval for a specific server. The default is the global timeout interval.. |
Step 3 | switch(config)# exit | Exits the global configuration mode and returns you to EXEC mode. |
Step 4 | switch(config)# show tacacs-server | (Optional) Displays the TACACS+ server configuration. |
Step 5 | switch(config)# copy running-config startup-config | (Optional) Copies the running configuration to the startup configuration |
switch# config terminal switch(config)# tacacs-server host 10.10.2.2 timeout 10 switch(config)# exit switch# n1000v# show tacacs-server Global TACACS+ shared secret:******** timeout value:10 deadtime value:0 total number of servers:1 following TACACS+ servers are configured: 10.10.2.2: available on port:49 timeout:10 switch# copy running-config startup-config
Use this procedure to configure a TCP port other than port 49 (the default for TACACS+ requests).
Before beginning this procedure, you must be sure you have done the following:
Command or Action | Purpose | |
---|---|---|
Step 1 | switch# configure terminal | Places you into global configuration mode. |
Step 2 | switch(config)# tacacs-server host {ipv4-address | host-name} port tcp-port | Specifies the TCP port to use. The allowable port range: 1 to 65535 The default is 49. |
Step 3 | switch(config)# exit | Exits the global configuration mode and returns you to EXEC mode. |
Step 4 | switch(config)# show tacacs-server | (Optional) Displays the TACACS+ server configuration. |
Step 5 | switch(config)# copy running-config startup-config | (Optional) Copies the running configuration to the startup configuration |
switch# configure terminal switch(config)# tacacs-server host 10.10.2.2 port 2 switch(config)# exit switch# show tacacs-server Global TACACS+ shared secret:******** timeout value:10 deadtime value:0 total number of servers:1 following TACACS+ servers are configured: 10.10.2.2: available on port:2 timeout:10 switch# copy running-config startup-config
You should know the following information:
Before beginning this procedure, you must be sure you have done the following:
Command or Action | Purpose | |||||
---|---|---|---|---|---|---|
Step 1 | switch# configure terminal | Places you into global configuration mode. |
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Step 2 | switch(config)# tacacs-server host { ipv4-address | host-name } test { idle-time minutes | password password [ idle-time minutes] | username name [ password password [ idle-time minutes] ] } | Configures server monitoring. The keywords and arguments are as follows:
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Step 3 | switch(config)# tacacs-server dead-time minutes | Specifies the duration of time in minutes before checking a TACACS+ server that was previously unresponsive. The default value is 0 minutes and the valid range is from 0 to 1440 minutes. |
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Step 4 | switch(config)# exit | Exits the global configuration mode and returns you to EXEC mode. |
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Step 5 | switch(config)# show tacacs-server | (Optional) Displays the TACACS+ server configuration. |
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Step 6 | switch(config)# copy running-config startup-config | (Optional) Copies the running configuration to the startup configuration |
switch# configure terminal switch(config)# tacacs-server host 10.10.2.2 test username pvk2 password a3z9yjqz7 idle-time 3 switch(config)# tacacs-server dead-time 5 switch(config)# exit switch# show tacacs-server Global TACACS+ shared secret:******** timeout value:10 deadtime value:5 total number of servers:1 following TACACS+ servers are configured: 10.10.2.2: available on port:2 timeout:10 switch# copy running-config startup-config
Use this procedure to configure the interval to wait before sending a test packet to a previously unresponsive server.
When the dead-timer interval is 0 minutes, TACACS+ servers are not marked as dead even if they are not responding. You can configure the dead time per group.
Before beginning this procedure, you must be sure you have done the following:
Command or Action | Purpose | |
---|---|---|
Step 1 | switch# configure terminal | Places you into global configuration mode. |
Step 2 | switch(config)# tacacs-server deadtime minutes | Configures the global dead-time interval. The default value is 0 minutes. The range is from 1 to 1440 minutes |
Step 3 | switch(config)# exit | Exits the global configuration mode and returns you to EXEC mode. |
Step 4 | switch(config)# show tacacs-server | (Optional) Displays the TACACS+ server configuration. |
Step 5 | switch(config)# copy running-config startup-config | (Optional) Copies the running configuration to the startup configuration |
switch# configure terminal switch(config)# tacacs-server deadtime 5 switch(config)# exit switch# show tacacs-server Global TACACS+ shared secret:******** timeout value:10 deadtime value:5 total number of servers:1 following TACACS+ servers are configured: 10.10.2.2: available on port:2 timeout:10 switch# copy running-config startup-config
Use the following command to display statistics for a TACACS+ host.
Command |
Description |
---|---|
show tacacs-server statistics {hostname | ipv4-address} |
Displays the statistics for a TACACS+ host. |
The following example shows a TACACS+ configuration:
switch# configure terminal switch(config)# feature tacacs+ switch(config-tacacs+)# tacacs-server key 7 "ToIkLhPpG" switch# (config-tacacs+)# tacacs-server host 10.10.2.2 key 7 "ShMoMhTl" switch# (config-tacacs+)# aaa group server tacacs+ TacServer server 10.10.2.2
This table only includes updates for those releases that have resulted in additions to the feature.
Feature Name |
Releases |
Feature Information |
---|---|---|
TACACS+ |
Release 5.2(1)IC1(1.1) |
This feature was introduced. |