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RADIUS server authentication: How does it work?

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A radius server makes use of a community protocol for distant person authentication and authorization. It’s a consumer/server protocol that enables a distant person to entry a community utilizing a shared secret (normally a password). RADIUS servers are usually positioned on the perimeter of a community and use port 1812 (UDP) or 1645/1813 (TCP).

RADIUS was initially developed by Livingston Enterprises, Inc. in 1991. It’s now an IETF commonplace (RFC 2865). The next are crucial issues to learn about RADIUS server authentication.

  •  RADIUS is a distant authentication dial-in person service

It was developed to offer centralized authentication, authorization, and accounting administration for networked units akin to routers and switches.

What does dial-in consult with right here? Dial-in is a kind of authentication that enables a person to hook up with a community remotely utilizing a cellphone line or different connection. RADIUS servers are used to handle person entry to a community. They can be utilized to regulate who can entry the community, what providers they will use, and the way a lot bandwidth they will devour.

  •  RADIUS is a substitute for TACACS and is usually used at the side of TACACS+ for authentication and authorization

The explanation for that is that RADIUS is usually used for distant entry, whereas TACACS+ is normally used for machine administration. Whereas each protocols can be utilized for each functions, RADIUS is normally the popular protocol for distant entry.

  •  A RADIUS server usually makes use of UDP port 1812 (or TCP port 1645/1813) to speak with purchasers

RADIUS servers usually pay attention on UDP port 1812 (or TCP port 1645/1813). When a RADIUS consumer sends a request to the server, it contains the key key within the request. The server makes use of this key to authenticate the consumer and authorize the request.

RADIUS is a consumer/server protocol, which signifies that every RADIUS consumer will need to have a corresponding RADIUS server. A RADIUS consumer is usually a community machine akin to a router or swap. A RADIUS server is a pc that runs the RADIUS software program and manages person entry to the community.

What this implies is that for a person to have the ability to entry the community, they have to first authenticate with the RADIUS server. The RADIUS server then authorizes the person’s entry to the community and controls what providers they will use.

  •  RADIUS makes use of a consumer/server structure

The RADIUS server is accountable for authenticating customers and sustaining their account info, whereas the RADIUS consumer is usually a community machine that forwards authentication requests to the server. The explanation this distinction issues is that it permits the server to be centrally positioned and managed, whereas the purchasers could be distributed all through the community. This structure additionally makes it attainable for the server to authenticate customers in opposition to a number of databases, akin to an LDAP server or an area file.

The implications of this are that if the server goes down, the whole community might be unavailable to customers. For this reason you will need to have redundant RADIUS servers in a manufacturing surroundings.

  •  A RADIUS server can authenticate customers in opposition to a number of databases

RADIUS helps a number of authentication strategies, together with PAP, CHAP, MS-CHAP, and EAP. PAP is the only authentication methodology and sends the username and password in clear textual content. CHAP encrypts the password however sends it over the community in plain textual content. MS-CHAP encrypts each the username and password. EAP is a safer authentication methodology that makes use of digital certificates.

  •  RADIUS makes use of UDP for transport

RADIUS makes use of UDP as its transport protocol. UDP is a connectionless protocol, which signifies that every packet is shipped independently and doesn’t require a connection to be established beforehand. This makes RADIUS very scalable, as it will probably help numerous purchasers with out requiring numerous assets on the server.

It issues that RADIUS makes use of UDP for transport as a result of UDP is a much less dependable protocol than TCP. Because of this RADIUS packets could be dropped or misplaced in transit. Nonetheless, that is normally not an issue as a result of RADIUS makes use of retransmission and error checking to make sure that packets are delivered reliably.

  •  The RADIUS server will need to have a shared secret with the purchasers

The RADIUS server and purchasers will need to have a shared secret, which is used to encrypt and decrypt packets. This shared secret is usually a password or phrase that’s identified solely to the server and purchasers. With out the shared secret, an attacker wouldn’t be capable to learn or modify the packets being exchanged between the server and purchasers.

  •  RADIUS makes use of Entry-Request and Entry-Settle for packets

When a consumer sends an authentication request to a RADIUS server, it does so utilizing an Entry-Request packet. The server then responds with an Entry-Settle for or Entry-Reject packet, relying on whether or not the authentication was profitable. If the authentication was profitable, the server can even embrace an Entry-Problem packet, which accommodates a problem that the consumer should reply to show its id.

  •  RADIUS can be utilized for AAA

RADIUS can be utilized for AAA, which stands for Authentication, Authorization, and Accounting. Authentication is the method of verifying a person’s id, authorization is the method of figuring out what assets a person is allowed to entry, and accounting is the method of monitoring and billing for a person’s utilization.

AAA is a standard safety mannequin that’s used to regulate entry to community assets.

  •  RADIUS is standardized by the IETF

RADIUS is a standards-based protocol, which signifies that it’s outlined by an Web Engineering Activity Power (IETF) specification. The newest model of the RADIUS specification is RFC 2865, which was printed in June 2000.

  •  RADIUS is usually utilized by ISPs

RADIUS is usually utilized by Web service suppliers (ISPs) to authenticate and authorize customers who’re making an attempt to entry the web. RADIUS can be utilized by company networks to authenticate and authorize customers who’re making an attempt to entry the community.

  •  There are a couple of completely different RADIUS implementations

There are a couple of completely different RADIUS implementations, together with FreeRADIUS, Microsoft NPS, and Cisco ACS. FreeRADIUS is the most well-liked open-source RADIUS server. Microsoft NPS is the RADIUS server included in Home windows Server. Cisco ACS is a business RADIUS server from Cisco Techniques.


These are crucial issues to learn about RADIUS server authentication. RADIUS is a crucial a part of many community safety methods, and understanding the way it works is crucial for anybody who’s accountable for managing a community.



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