Is it possible to have 2 tacacs server on same network, if the first server auth fail,
then, the second one will do the auth ?
If you use ACS as your tacacs server, you can synchronize the user databases between the multiple tacacs servers.
If you don't synchronize them then you can have the same username with different passwords/policies on the different ACS boxes. It's all a matter of how you configure your boxes, with synchronization or not.
Sure is. Just configure your network devices to fail over to the alternate server if the first is unavailable.