Remote Authentication Dial In User Service

Remote Authentication Dial In User Service (RADIUS) is an AAA (authentication, authorization and accounting) protocol for applications such as network access or IP mobility. It is intended to work in both local and roaming situations.

Some ISPs (commonly modem, DSL, or wireless 802.11 services) require you to enter a username and password in order to connect to the Internet. Before access to the network is granted, this information is passed to a Network Access Server (NAS) device over the Point-to-Point Protocol (PPP), then to a RADIUS server over the RADIUS protocol. The RADIUS server checks that the information is correct using authentication schemes like PAP, CHAP or EAP. If accepted, the server will then authorize access to the ISP system and select an IP address, L2TP parameters, etc.

The RADIUS server will also be notified if and when the session starts and stops, so that the user can be billed accordingly; or the data can be used for statistical purposes.

Additionally RADIUS is widely used by VoIP service providers. It is used to pass login credentials of a SIP end point (like a broadband phone) to a SIP Registrar using digest authentication, and then to RADIUS server using RADIUS. Sometimes it is also used to collect call detail records (CDRs) later used, for instance, to bill customers for international long distance.

RADIUS was originally developed by Livingston Enterprises for their PortMaster series of Network Access Servers, but later (1997) published as RFC 2058 and RFC 2059 (current versions are RFC 2865 and RFC 2866). Now, several commercial and open-source RADIUS servers exist. Features can vary, but most can look up the users in text files, LDAP servers, various databases, etc. Accounting tickets can be written to text files, various databases, forwarded to external servers, etc. SNMP is often used for remote monitoring. RADIUS proxy servers are used for centralized administration and can rewrite RADIUS packets on the fly (for security reasons, or to convert between vendor dialects).

RADIUS is a common authentication protocol utilized by the 802.1x security standard (often used in wireless networks). Although RADIUS was not initially intended to be a wireless security authentication method, it improves the WEP encryption key standard, in conjunction with other security methods such as EAP-PEAP.

RADIUS is extensible; most vendors of RADIUS hardware and software implement their own dialects.

The DIAMETER protocol is the planned replacement for RADIUS. DIAMETER uses TCP while RADIUS uses UDP as the transport layer.

RADIUS uses ports 1812 & 1813 for Authentication and Accounting respectively.