RADIUS vs. Diameter Protocol: What’s the Difference?

Last updated on March 3, 2025

The main difference between RADIUS and Diameter is that RADIUS is a protocol mainly used to provide centralized access to a network, while Diameter is a protocol that is mainly used in the telecommunication industry. Read on to learn more about RADIUS vs. Diameter.

What is the RADIUS protocol?

Remote Authentication Dial-In User Service (RADIUS) is a networking protocol that exchanges authentication, authorization, and accounting (AAA) data between a client and a server.

Though ubiquitous in the IT world, RADIUS has some disadvantages:

• Poor scalability
• Not very extensible
• Lacks features such as support for agents, capability negotiation, and error messages.

Experts devised several new protocols to correct these faults and replace RADIUS. One of them is Diameter.

What is the Diameter protocol?

Diameter is a networking protocol that exchanges authentication, authorization, and accounting (AAA) data between two parties. Unlike RADIUS, which only allows a client to deliver a request to the server, Diameter also allows sending a request from a server to a client.

Initially, Diameter was developed as a better version of RADIUS meant to replace it. With time, however, the use cases for these two protocols diverged. Diameter is mainly used in the mobile world. In contrast, RADIUS is used for everything else. Most switches and access points support RADIUS. However, not many of them support Diameter.

What’s the Difference Between RADIUS and Diameter protocol?

RADIUS	Diameter
Open standard described in RFC 2865	Open standard described in RFC 6733.
Simple but less extensible.	Complex but more flexible.
RADIUS uses UDP as the transmission protocol.	Diameter uses TCP or SCP as the transmission protocol.
RADIUS is connectionless, which means it does not require prior session creation.	Diameter is a connection-oriented protocol.
RADIUS operates on UDP port 1812 or 1645 for authentication and port 1813 or 1646 for accounting.	Diameter operates on TCP and SCTP port 3868.
RADIUS provides Hop-by-Hop security.	Diameter provides Hop-by-Hop authentication (thanks to IPsec or TLS). Diameter can also provide End-to-End security.
In RADIUS, there is no support for agents, as RADIUS assumes a direct connection.	Diameter supports agents (Relay, Proxy, Redirect, and Translation).
RADIUS supports client-initiated messages. Support for server-initiated messages is optional.	Diameter supports client-initiated messages and makes support for server-initiated messages mandatory.
In RADIUS, the server cannot send requests to a client.	In Diameter, the server can also deliver a request to a client.
RADIUS does not support capability negotiation, error messages, and mandatory/non-mandatory flags for attributes.	Diameter supports application and security level negotiation, error messages, and mandatory/non-mandatory flags for attributes.
RADIUS has poor scalability, which makes it a disfavored choice for large networks.	Diameter provides good scalability.

Implementing Multi-Factor Authentication (MFA) for RADIUS

Relying solely on single-factor authentication methods, such as passwords, is inadequate due to the increasing sophistication of cyber threats. Integrating multi-factor authentication (MFA) with the RADIUS protocol enhances security by requiring multiple forms of verification, thereby reducing the risk of unauthorized access.

Why Implement MFA for RADIUS?

• Enhanced Security: MFA adds an extra layer of protection by requiring additional verification methods beyond just a password, making unauthorized access more difficult.
• Regulatory Compliance: Many industries mandate the use of MFA to comply with data protection regulations, ensuring that only authorized users can access sensitive information.
• User Trust: Implementing MFA fosters trust among users, assuring them that their accounts and data are secure.

How to Integrate MFA with RADIUS?

Enabling MFA for RADIUS involves the following steps:

• Choose an MFA Solution: Select an MFA provider that supports RADIUS protocol integration like Rublon MFA.
• Configure the RADIUS Proxy Server: Set up your RADIUS Proxy Server like Rublon Authentication Proxy to create a bridge between your FreeRADIUS or Active Directory user source and the Rublon API. This connection ensures that your users are challenged for multi-factor authentication during login.
• Update Network Settings: Modify the settings of network devices (such as routers, firewalls, and VPNs) to direct authentication requests to the newly configured Authentication Proxy.
• Test the Configuration: Conduct thorough testing to ensure that the MFA integration works seamlessly, providing both security and usability.

Looking for MFA for RADIUS-Enabled Routers, Firewalls, and VPNs?

Rublon empowers VPNs and applications that support the RADIUS protocol by enabling strong Multi-Factor Authentication (MFA) for all user logins. You can use a RADIUS server or Active Directory as your identity provider (IdP).

Get on the MFA train today by starting a Free 30-Day Rublon Trial:

Summing up RADIUS vs. Diameter protocol

Both RADIUS and Diameter are AAA protocols that exchange information between a Network Access Server (NAS) and a shared Authentication Server. Still, RADIUS and Diameter have many differences. RADIUS is a protocol for centralized network access. In contrast, Diameter is a protocol for telecommunication networks, such as LTE.