By using an authorization script, we can make tac_plus to do very granular authentication, having different permissions granted to different switches defined by user, source IP and device IP. However, writing/editing a script to change access can be difficult. Hard coded authorization scripts are not very flexible, hence, I decided to implement a python program to facilitate flexibility. I believe it may be included in the next tac_plus.
Configuration is fairly simple; as an example, let’s say I wanted to have user Homer have full access to 192.168.1.1 and 10.1.1.0/24, but only do show commands for everything else in 10.0.0.0/8. For the heck of it, let’s say we only want Homer to connect from 192.168.1.0/24, but never 192.168.1.4, which host can only do the show commands. The config file would simply be as follows:
[users]
homer =
simpson_group
television_group
[simpson_group]
host_deny =
192.168.1.4
host_allow =
192.168.1.*
device_permit =
192.168.1.1
10.1.1.*
command_permit =
.*
[television_group]
host_allow =
192.168.1.*
device_permit =
10.*
command_permit =
show.*
Example line to put in tac_plus user or group:
after authorization “/usr/bin/python /root/do_auth.pyc -i $address -u $user -d $name -l /root/log.txt -f /root/do_auth.ini”
(that’s all ONE line)
On my server, I set homer’s password file to /etc/passwd and enable cracklib. Homer can change his password any time he wants just by logging to Linux and typing passwd – he does not need root access. Homer is also forced to pick a secure password, and has different access based on different devices. Given these abilities, combined with the quick administration, tac_plus makes purchasing Cisco’s tacacs server seem like a waste of money.
In the future, I may alter the program to have the ability to send back additional av-pairs, and/or completely new av-pairs. However, currently I simply don’t need this feature as I pass these pairs back to tac_plus. The source code is very simple and is GPL’ed for all to see at: http://pastie.org/506002 and is available in compiled/ready to use form here. For more instructions, you can download this compiled pyc and type “python do_auth.pyc” If I ever get time, I may consider a gui or web interface.
Update: New version 1.2
Fixed pix. Also, apparently there is a bug in the pix that makes it necessary to add a 0.0.0.0 to your allowed hosts.
-Dan Schmidt
Till then:
Cisco Application Control Engine modules are really separate devices from the “mother” switch, only suckling power and connectivity. These devices need their own authentication schemes. It’s pretty easy to turn on TACACS+ authentication and accounting (no authorization again. Why do vendors insist on only doing 1 or 2 As and not 3?).
ACE modules needs a specific optional av-pair in the “exec” service in TACACS+ to authenticate. You can put this in a group or user stanza:
