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RADIUS Authentication Protocol

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The Remote Authentication Dial-In User Service (RADIUS) server implements a client-server protocol, based on the Internet Engineering Task Force (IETF) Request for Comments (RFCs) 2865 and 2866, that enables remote access clients to communicate with a central server to gain access to a network. The RADIUS server authenticates users, authorizes their requests to services, and writes accounting data.

Typical clients in a RADIUS environment are a terminal server, authenticating LAN device, or wireless access point.

The RADIUS server consists of three services:

  1. Authentication
  2. Authorization
  3. Accounting
These services work together with either UNIX authentication, a local database, or a Lightweight Directory Access Protocol (LDAP) directory to provide authentication information. The RADIUS authentication server daemon provides security and user authentication for remote connections to the network. It also handles authorization, which specifies what services are available, and in some configurations, how network access is accomplished. The RADIUS accounting server daemon tracks when and how long remote connections are connected to the network.

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.

When you connect to an ISP using a modem, DSL, cable or wireless connection, for some providers, you must enter your username and password. 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.

There are many free Radius implementations. Among them:

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[Aug 21, 2008] Setting Up A FreeRadius Based AAA Server With MySQL & Management With Daloradius HowtoForge - Linux Howtos and Tutorials

This tutorial explains how you can set up a FreeRadius (1.1.7) server with Wifi authentication and accounting in conjunction with MySQL & web management with Daloradius on Ubuntu 8.04 (LTS) This howto should work for a newbie. Production deployment is also possible with minor tweaking. But as usual I do not guarantee anything & take no responsibilities if something goes wrong.

[Jun 20, 2008] RAdmin


RAdmin is a Web-based Radius user administration package that works with Radiator and any SQL database on any platform. It provides pages that allow you to add/change/remove users, and to view usage summaries, online modems, service profiles, per-user and per-service Radius check and reply items, and more. The pages available to end users provide usage summaries and facilitate password changing. It supports optional Vasco Digipass tokens.

Open System Consultants, Mike McCauley <mikem [at] open [dot] com [dot] au> [contact developer]

[Mar 10, 2005] FreeBSD and RSA SecurID Authentication


This post is really for archival purposes in the event that someone
else is looking into centralized authentication with RSA SecurID and
FreeBSD (or any other *nix platform for that matter)..

The organization I currently work for has a large ($$$) investment in
RSA SecurID (for VPN use mainly) and like most technology deployments
around here it is not used to it's full capability.  With the onset of
SOX and the like, password use/policy/management has become a rather
large headache.  So for us, SecurID made sense (at least in theory):
centralized, one time passwords.

( Yes, I know there are other options for centralized Unix account
administration, but to this point we have only used local accounts and
some SecurID.  And our goal was to leverage existing infrastructure. )

Our Unix environment, in a phrase: "you build it, we'll run it".  So
it was off to RSA to see what agents/clients are currently available. 
Now we've be running older versions, in a limited capacity, of the RSA
agents for some time (sdshell: a shell that requires SecurID
authentication), but the support is limited (HP-UX, Solaris, AIX).
Then I noticed an available PAM module, joy!  But the joy was short
lived, it only supports Solaris and RHE Linux.

So, when all else fails you head to google...  What I found was a lot
of people in the same boat (on various platforms).  I found a few
possible solutions, but not anything I felt confident about.  So back
to square one.

Then I remembered that our VPN environment uses SecurID, but via
RADIUS.  Ahhh...  Knowing that FreeBSD already had a RADIUS PAM
module, it was my first test platform (5.3).  Once everything was
configured it worked like a charm.  Now for the rest of the
environment...  Linux: Not a Problem (most distros come with the
FreeRadius PAM module), Solaris: Used PAM module from FreeRadius,
HP-UX: Also used module from FreeRadius (it was a bear to get
compiled), AIX: Haven't gotten to this one yet, but I have my fingers
crossed ;-).  Everything at this point appears to work well and the
best part is that the solution/setup is the same for all!

A 'very quick' overview of the configuration...   

1 - A RSA ACE Server running and configured with RADIUS (currently
runs on Solaris/HP-UX and WIndows?)
2 - A client server with a Radius PAM Module
3 - Create a 'Shared Secret'. 
4 - Configure the RSA ACE/RADIUS server and the client server with
'shared secret'.  (PAM module uses /etc/radius.conf for 'shared
secret', servername, etc)
5 - Configure PAM/sshd (or whatever PAM aware services) to require
RADIUS authentication
6 - Configure your local users. (local username must be there SecurID username)

here are some links...  (limited documentation here, it's all on
the install cd's)
... and of course various local manpages.

A quick note on security...

RADIUS is not the most secure protocol out there.  As a matter a fact
data is hidden via a md5  hash. (more details: ).  But our feeling was since
it's SecurID and the generated passcode is only used one time, the
risk is acceptable/minimal! (better then a lame password any day ;-)


RADIUS Extension Guide Introducing RADIUS

PAM Module

You can use the plugable authentication module (PAM) to offer authentication mechanisms such as Kerberos, RSA or smart cards on top of RADIUS. The PAM module is part of the Solaris operating system.

For general information on the PAM authentication modules and API, refer to the pam(3) man page. For information on configuring PAM authentication modules, refer to the pam.conf(4) man page.

For information on configuring the RADIUS server to operate with the PAM module, refer to "Configuring RADIUS to Use PAM". Solaris Bandwidth Manager 1.6 System Administration Guide

The RADIUS server provided with Sun Directory Services 3.1 offers an authentication service for remote users. For full information on the RADIUS server, refer to the documentation delivered with Sun Directory Services 3.1.


The RADIUS server provided with Sun Directory Services 3.1 is an authentication and authorization information server for a Network Access Server (NAS). A NAS is a device that provides an access point to the network for remote users connecting using SLIP, PPP or any other remote access protocol. The NAS transmits the information provided in the connection request from the remote user to the RADIUS server. The RADIUS server checks this information against the entry for the remote user in the directory. It then returns to the NAS an authorization or denial for the remote user connection. It can also provide the appropriate connection parameters for the remote user connection.

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Introducing RADIUS


The RADIUS protocol is currently defined in:

Other relevant RFCs are:




GNU Radius Reference Manual: Client Package

Client Package. Beside the Radius server and accompanying utilities, GNU Radius provides a set of utilities to be used as Radius clients. ... - 4k -

RADIUS Clients - FreeRADIUS Wiki

pyrad is a Python implementation of a RADIUS client as described in RFC2865. ... Radiusclient is a framework and library for writing RADIUS clients. ... - 13k - Cached - Similar pages



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