Cisco Nexus 5000 Series Switch CLI Software Configuration Guide, NX-OS 4.0(1a)N1 (OL-16597-01, January 2009)

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Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
OL-16597-01
Chapter 18 Configuring TACACS+
Information About TACACS+
• Connection parameters, including the host or client IP address (IPv4 or IPv6), access list, and
user timeouts
Default TACACS+ Server Encryption Type and Preshared Key
You must configure the TACACS+ preshared key to authenticate the switch to the TACACS+ server. A
preshared key is a secret text string shared between the Nexus 5000 Series switch 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 on the Nexus 5000 Series switch to use.
You can override the global preshared key assignment by explicitly using the key option when
configuring an individual TACACS+ server.
TACACS+ Server Monitoring
An unresponsive TACACS+ server can delay the processing of AAA requests. A Nexus 5000 Series
switch can periodically monitor an TACACS+ server to check whether it is responding (or alive) to save
time in processing AAA requests. The Nexus 5000 Series switch marks unresponsive TACACS+ servers
as dead and does not send AAA requests to any dead TACACS+ servers. A Nexus 5000 Series switch
periodically monitors dead TACACS+ servers and brings them to the alive state once they are
responding. This process verifies that a TACACS+ server is in a working state before real AAA requests
are sent its way. Whenever an TACACS+ server changes to the dead or alive state, a Simple Network
Management Protocol (SNMP) trap is generated and the Nexus 5000 Series switch displays an error
message that a failure is taking place before it can impact performance. See Figure 18-1.
Figure 18-1 TACACS+ Server States
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.
No
response
Test
Test
Idle timer
expired
Directed
AAA request
Dead timer expired
Response from
remote server
AAA packets
sent
Alive
Alive and
used
Dead and
testing
Alive and
testing
Dead
Application
request
Process
application
request
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