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ACS appliance failover( High Availibility) documentation

Nilaykumar Patel


I have to configure Cisco ACS for Active/Passive role. I am looking for some documentation on that on cisco website but can not find it.

Can anyone suggest me proper best practice documentation ?

Thank you,


3 Replies 3


Hi there,

The ACS doesn't work like an ASA where you can have one active and the other standby. What you can do is to have one primary and another as the secondary, where depending on your TACACS+/Radius commands the authentication server role will change, for example:

tacacs-server host key xxx

tacacs-server host key xxx

This configuration means that the router will try to contact always, but if this server goes down, the router will try to contact until the is up again.

So as you can see the ACS servers doesn't have control about which will be the active server, only which is the primary and which is the secondary (primary and secondary is important because you configure the settings in the primary and this one replicates those changes to the secondary).


Hello Nilay.

Mauricio is right. To expand his answer, if you have several  ACS appliances only one of them is primary and all the other ones are  secondary.

"Primary" and "secondary" concepts are different from "active" and "standby" concepts. All ACS are "active".

The  switch configuration tells the switch which ACS to talk to. It can be  one, two, three, any number of ACS. Also if there are more than one ACS,  the switch configuration gives the preference to the first ACS declared  in the configuration. Only if the first ACS doesn't respond at all  then the switch will try to talk to the second ACS declared. Only if the  second ACS doesn't respond at all then the switch will try to talk to  the third ACS and so on.

here's an example of switch configuration with three ACS

radius-server host key MYPASSWORD

radius-server host key MYPASSWORD

radius-server host key MYPASSWORD

radius-server vsa send authentication

aaa new-model


aaa group server radius ACS





aaa authentication dot1x default group ACS

aaa authorization network default group ACS

aaa accounting dot1x default start-stop group ACS

I configured distributed deployment explained in above document and it works fire. Thank you for your help.


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