!!! Overview
[{$pagename}] ([RADIUS]) is a [network] [protocol] defined in [RFC 2058] that provides centralized [Authentication], [Authorization], and [Accounting] ([AAA]) management for users who connect and use a network service. 

[{$pagename}] was developed by Livingston Enterprises, Inc. in [1991|Year 1991] as an access server [authentication] and [accounting] [protocol] and later brought into the [Internet Engineering Task Force] ([IETF]) standards

[{$pagename}] can use either [TCP] or [UDP] as transport. Network [Access Proxy], the gateways that control access to a network, usually contain a RADIUS client component that communicates with the RADIUS server.[{$pagename}] is often the backend of choice for 802.1X authentication as well.

The [{$pagename}] [server] then returns one of three responses to the [Access Proxy]:

* Access Reject - The [Access Request] is unconditionally denied access to all requested network resources. Reasons may include failure to [Authentication] or an unknown or [Administratively Disabled] user account.
* Access Challenge - Requests additional information from the user such as a secondary password, [PIN], [token], or [Smart Card]. Access Challenge is also used in more complex authentication dialogs where a secure tunnel is established between the user machine and the Radius Server in a way that the access [credentials] are hidden from the [Access Proxy].
* Access Accept - The [Access Request] is granted access. Once the user is authenticated, the RADIUS server will often check that the user is authorized to use the network service requested. 

A given [Entity] may be allowed to use a company's [wireless] [network], but not its [VPN] service, for [example]. Again, this information may be stored locally on the RADIUS server, or may be looked up in an external source such as [LDAP] or [Microsoft Active Directory] or a [Policy Retrieval Point] and [Policy Information Point]

!! More Information
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