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Network Authentication Protocols: RADIUS, TACACS+

Last Updated : 21 Mar, 2024
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Network authentication protocols are known as methods that are used to verify the identity of the users or the devices that are written to access a particular network. these protocols are used to make sure that only the authorized users of the devices are granted access while making sure the unauthorized users are out. so in this article, we will understand two of the most commonly known protocols used for network authentication: RADIUS & TACAS+

What are Authentication Protocols?

The authentication protocols have a procedure in which they involve the exchange of credentials or cryptographic keys between the client which can be either a user or the device and the authentication server the main reason behind using a protocol such as the network authentication protocol is to make sure that we only allow authorized users to access the server.


Network Authentication Protocols: RADIUS, TACACS+

The network authentication protocols serve as the backbone of the secure network access which makes sure that only the authorized users or the authorized devices can connect and interact with the network’s resources.

What Are Network Authentication Protocols?

Let’s assume that there is a single administrator present who wants to access hunted routers and for simplicity let’s also assume that the local database of the device is the database that is to be used for the authentication or password what this means is that the administrator will have to make same user accounts for many times this is not a problem but if he wants to keep different password as well as different user name for each of the user then it will become hectic task because he will have to do it manually for each of the devices, to make this process more easy and convenient access control server is used which provides a centralized management system and in this all the password and usernames are stored there are many two protocols which are used by the acs with the help of clients to serve this purpose:

  • TACAS+

So let’s understand each of these protocols:

RADIUS Protocol

The full form of the RADIUS protocol is remote authentication dial in user service and it is a security protocol which is used in the AAA framework in order to provide an authentication system for the users which is centralized, for the users want to gain access to the network.

It uses UDP as a transmission protocol and it is a open standard protocol for AAA framework which means that it can use between the Cisco acs server and any of the vendor device possible.

Note: It uses UDP port number 1812 for authentication and authorization and 1813 for accounting.

Working of RADIUS Protocol

Working on the RADIUS protocol is very simple when the other device wants to access the network access server which is a client of the RADIUS it will simply send an access request as a message to the ACS server in order to gain matching credentials in return, After this the server provides a message which is known as access-accept message and this message is only provided if the credentials are valid if the credentials are invalid then the client receives access-reject as message.

Advantages of RADIUS Protocol

Now that we have understood the working of the RADIUS protocol let’s also understand the advantages of the RADIUS protocol:

  • it is an open standard, it can be used between the other devices as well.
  • This protocol has better accounting support than the TACACS+
  • The RADIUS protocol provides centralized authentication and authorization.
  • Radias provides flexible user management.
  • The RADIUS protocol is known to be highly scalable which means that it can support large networks which have many devices and many users.

Disadvantages of RADIUS Protocol

Now that we have looked at some of the benefits or advantages of using the RADIUS protocol let’s also look at some of the disadvantages which we may face if we are going to use the RADIUS protocol:

  • The RADIUS protocol uses udp which makes it less reliable than TACACS+
  • In this protocol no explicit command authorization can be implemented in any way.
  • The RADIUS protocol only encrypts the password which means that it cannot protect other data such as the usernames.
  • This protocol is very vulnerable to other types of attacks such as spoofing as well as dictionary attacks.

TACACS+ Protocol

The full form of the TACACS+ stands for terminal access controller access control server, it is a protocol which has similarities to the RADIUS protocol, which means that it is a security protocol and it is also used in the AAA framework, it is used to to provide centralized authorization to various types of users who need to gain access of the network.

The Cisco company has developed the protocol for AAA framework which means that it can be used between the Cisco device and Cisco ACS server, This protocol uses tcp as transmission protocol and it uses the TCP port 49.

Working of TACACS+ Protocol

The client of the TACACS+ protocol is called the network access device (NAD) it is also called network access server (NAS) the network access device contacts the TACACS+ server in order to obtain prompt of the username and it does this using the CONTINUE message.

After this the user simply enters a user name and then the network access device makes a contact to the protocol server again in order to obtain the password prompt after this the user simply enters the password and then the password is sent to the protocol’s server.

Advantages of TACACS+ Protocol

Now that we have understood the basics about this protocol, let’s look at some of the advantages that this protocol offers:

  • It provides better control then the RADIUS protocol because it allows the network administrator to easily define what commands a user can run.
  • All the AAA packets are more encrypted rather than just being passwords.
  • TACACS+ protocol uses the TCP connection instead of the UDP connection and the TCP guarantees the communication between both the client and the server.

Disadvantages of TACACS+ Protocol

  • As we discussed that it is a cisco proprietary which means that it can only be used in the Cisco devices.
  • This protocol has less support for the accounting as compared to RADIUS.

Difference Between RADIUS and TACACS+ Protocol

Now that we have understood about both of the network protocols (RADIUS and TACACS+) so lets take a look at the difference between these two protocols so that we have a better understanding:





It uses the UDP protocol.

It uses the TCP protocol.


This protocol supports PAP, CHAP, MS-CHAP, EAP.

This protocol upports CHAP, PAP, MS-CHAP, EAP.


In this protocol the passwords are encrypted during transmission.

In this protocol the entire session is encrypted.


There is limited to authentication and accounting in this protocol.

This protocol supports authentication, authorization as well as authentication.

Access Control

It is limited to basic access control policies.

It offers more access control policies.


This protocol is less secure due to weaker encryption

This protocol is more secure due to session encryption and separate authentication and authorization.

Session Management

This protocol is stateless.

This protocol is stateful.


This is commonly used in smaller networks.

This protocol is preferred in larger and more complex.


In conclusion, we learned about two of the most important protocols are used for the network authentication and we looked at their inner working to understand how each of these protocols are different from one another after this we also looked at how these protocol are important for the network authentication and then we compared them by looking at the advantages and disadvantages among each of these protocols and difference table as well.

Network Authentication Protocols: RADIUS, TACACS+ – FAQs

What are the advantages of using RADIUS authentication?

The RADIUS protocol has several advantages, including centralized management of user accounts and credentials, it also offers enhanced security through encryption of authentication data and it has the support for multiple authentication methods.

Can RADIUS and TACACS+ be used together?

Yes, both the RADIUS and TACACS+ can work together in some cases, for example, RADIUS can handle general user authentication while the TACACS+ protocol can manage the privileged access to network devices.

What encryption standards do RADIUS and TACACS+ support?

Both the RADIUS and TACACS+ supports encryption for securing the communication between clients and servers, some of the common encryption standards for these two protocol includes – Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS).

Do RADIUS and TACACS+ support multi-factor authentication (MFA)?

Yes, both protocols can work with any MFA systems in order to provide an additional layer of security, this helps the users to authenticate using multiple factors, such as passwords, biometrics, or security tokens.

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