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Radius and Tacacs server for Authentication

Radius and Tacacs server for Authentication

When we study for certification regarding Cisco, we encounter topic like Radius or Tacacs Server many times. You all know what are these and when to use them. But will it be beneficial to setup Radius or Tacacs authentication in real production network ?

Suppose you have 20 - 30 devices and there are three network administrator handling those devices in your company. One day you get a news that one of the network engineer is leaving an organization. To comply with company's security policy, you need to delete his/her Login credentials from all 20 - 30 devices. It hardly takes 20 - 30 Min to do that. No problem ! All is well till now.

Now imagine a different scenario in which you are working in even bigger organization which has around 2000 devices and has large network team around 15 - 20 Network admins. Each one of them has different access permissions on the network devices and some of them only have access permissions to limited number of network  devices. Meanwhile some network admins are leaving your organization and some are joining. Hey friends you all know how attrition works in today's corporate world !! Now how you will going to manage these users credentials in all 2000 Devices. I am pretty sure you will not going to sit and configure login access credentials for all different users with different access level on all the devices. It such a mammoth task to manually manage(that includes creation/deletion/modification) these login credentials information in this manner for each user on each individual device for such a large network base. Isn't it!!

Here Authentication server like Radius or Tacacs comes to our rescue. So now I will explain how it works. Broadly speaking, each network device will go to your Authentication server to find whether the user have rights to login in device or not. There are many other task which Radius or Tacacs server do. Like AAA :

A - Authentication

A- Authorization

A - Accounting

A - Authentication :

Checks the user and password to login in the network devices. Basically verifies the authenticity of the user trying to access the device by checking the login credentials.

A - Authorization:

Checks that user regarding the rights he/she has. Like Privilege level 0 - 15 in Cisco world. This feature ensures only the users who are authorized to access the specific content can access it on the given device.

A- Accounting :

It keeps track of what  type the command user is executing on network devices when they are successfully login into the device. So it will make user accountable for the way he/she is using network devices by keeping the record of the activities user is performing over the network device.

This Authentication server is same like AD(Active Directory Server) in windows world where user are authenticated via AD to login into the windows machine.

Basically there are two types of Authentication server which are available:

Radius : It is open source and can be implemented for free.

Tacacs : It is Cisco proprietary. Have to purchase it from Cisco. It is very costly solution.

Some of the free Open source Radius server are :

  1. FreeRadius


And many More. Such is the benefit of having open source softwares.... You can easily google it.

For Tacacs server , you need to purchase ACS(Access Control Server) server from Cisco. This comes as a hardware appliance or ISO file which can be installed in any Virtual environment. You can download 60-days Evaluation version for practice, demo or Lab.

Closing Note : If you have small Network then there is no need of Authentication server as such. But if you have very large network with big team of engineers to manage it than it is advisable to have Authentication server Like Radius or Tacacs. It is easy to manage and more secure  solution to implement.

For any queries related to this topic, you can leave your comments below in the section provided.  For further blogs related to Networking please subscribe the blog.

Keep networking till we meet next!!!! :)


  1. Thanks for your post.Please can ACS be use to authenticate wireless user on a network.
    Also, I will like to know if ACS can be use with user registered on AD for authentication

  2. Thanks for your Post. I never configured ACS integration with AD. But you can check this Cisco Doc :

  3. TACACS+ can be downloaded free of charge and used without charge, but you have to install it on a linux based machine.


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