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The FreeRADIUS project has developed an open source RADIUS server.
Based on current statistics, there are over 50,000 deployments of the
software. These deployments include small sites with 10 users,
large-scale enterprises with tens of thousands of users, and
carrier-class deployments with over 10 million users. In total, the
sites that we know are using FreeRADIUS support nearly 100 million
users. The only other servers that come close in terms of market
share and/or number of sites are ACS and IAS.
The server scales easily from embedded systems with small amounts
of memory to systems with millions of users. It is fast, flexible, configurable, and supports more
authentication protocols than most commercial servers. It includes
support for SQL, LDAP, RADIUS Proxying, failover, load balancing, and
nearly 100 vendor dictionary files. It can perform authentications
via the PAP, CHAP, MS-CHAP, EAP-MD5, EAP-GTC, EAP-TLS, EAP-TTLS,
PEAPv0, LEAP, EAP-SIM, and Digest authentication protocols. It has
reached a stable, with incremental improvements added in
each release.
The project is growing to include a client library that is BSD licensed.
There is also a PAM library, and an
Apache module.
Features of the FreeRADIUS AAA Server
The FreeRADIUS server has a number of features which are
commonly found in RADIUS servers, and additional features which
are not found in any other free software server. Rather than doing
a feature by feature comparison, we will simply list some of the
features of the server, and let you decide if they satisfy your
needs.
Cross-platform issues and source code
The FreeRADIUS server has been compiled and tested to run on
the following platforms:
Linux (all versions)
FreeBSD
NetBSD
Solaris
MAC OSX
The server currently has support for the following
platforms, but has not been fully tested on them.
HP/UX
AIX
MINGW32, CygWin (Unix-style environment under Windows NT.)
SFU (or Interix, for Windows XP)
Unlike commercial servers, a large number of CPU and OS
architectures are have been verified to work, and are "supported"
via the users list. The drawback of
supporting so many variations of systems is that the steps
required to install the server can often be more than just
"install a package". We suggest that you look to your OS vendor
for a FreeRADIUS package for your system first, and if one was not
found, then build the server from source>.
Additional server configuration attributes
In addition to the RFC and VSA attributes defined above, the
FreeRADIUS server has a number of server configuration
attributes. These attributes allow you to control almost any
aspect of an incoming RADIUS request. You can use these attributes
to:
Append attributes to the request
Re-write any attribute of the request
Proxy or replicate the request to another RADIUS server,
based on any criteria, not just '@realm'.
Choose an authentication method to use for this
user.
Administer users by groups
Implement time of day access restrictions
Execute a local program
Limit the number of simultaneous logins by the user
All of the server configuration attributes can be used on
either authentication or accounting RADIUS requests. Most
servers limit this sort of configurability to authentication
requests only.
Selecting a particular configuration
It is often difficult to allow a users request to match a
particular configuration which should be used to reply to the
user. The FreeRADIUS server provides a wide range of methods to
select configurations.
The server can select a configuration based on any of the
following criteria:
Attributes which have a given value
Attributes which do not have a given value
Attributes which are in the request (independent of their
value)
Attributes which are not in the request
String attributes which match a regular expression
Integer attributes which match a range (e.g. <, >,
<=, >=)
Source IP address of the request. This can be
different than the NAS-IP-Address attribute
Group of NAS boxes. (These may be grouped based on Source
IP address, NAS-IP-Address, or any other configuration)
User-Name
a DEFAULT configuration
multiple DEFAULT configurations
Authorization methods
The following authorization types are some of the methods which
are supported by the server
Local files
Local DB/DBM database
LDAP
A locally executed program. (like a CGI program.)
Perl program
Python program
MySQL DB
PostgreSQL DB
Oracle SQL DB
any IODBC SQL DB
IBM's DB2
Authentication methods
The following authentication types are some of the methods which
are supported by the server
Clear-text password in local configuration file (PAP)
The server includes dialup_admin, a PHP4 based web
administration interface for the server. Dialup Admin
supports:
Users in LDAP database
Users and Groups in SQL database (MySQL or PostgreSQL)
Create, test, delete, change personal information, check accounting
and change dialup settings for a user
Accounting Report Generator
Bad Users facility to keep a record of users creating problems
Online finger facility
Test RADIUS server
Online Usage Statistics
Scripting Languages
FreeRADIUS contains plug-in modules which support
Perl, and
Python. These languages allow
scripts to modify RADIUS requests and responses in a very efficient
and simple manner.
RFC Compliance
FreeRADIUS strives to be conformant to relevant RFCs.
RFC 2868 RADIUS Attributes
for Tunnel Protocol Support
RFC 2867 RADIUS Accounting
Modifications for Tunnel Protocol Support
Installing and Testing FreeRADIUS
tar -zxvf freeradius-1.0.2.tar.gz - extract it with gunzip and tar
./configure
make
make install - run this command as root
radiusd or - start RADIUS server
radiusd -X - start RADIUS server in debug mode
radtest test test localhost 0 testing123 - test RADIUS server
If radtest receives a response, the FreeRADIUS server is working.
Another free tool, NTRadPing, can test authentication and
authorization requests from Windows clients. It can display detailed responses
such as attributes value sent back from the RADIUS server.
Configuring FreeRADIUS
Configuring the RADIUS server consists of configuring the server, the client, and the user (both for authentication and authorization). There can be different configurations of the RADIUS server for different needs; fortunately most of the configurations are similar.
Configuring the server
FreeRADIUS configuration files are usually stored in the /etc/raddb folder. First we need to modify the radiusd.conf file as shown.
Modifying radiusd.conf
1) Global settings:
log_auth = yes - log authentication requests to the log file
log_auth_badpass = no - don't log passwords if request rejected
log_auth_goodpass = no - don't log passwords if request accepted
2) LDAP Settings:
modules {
ldap {
server = "bluepages.ibm.com" - the hostname or IP address of the LDAP server
port = 636 - encrypted communications
basedn = "ou=bluepages,o=ibm.com" - define the base Distinguished Names (DN),
- under the Organization (O) "ibm.com",
- in the Organization Unit (OU) "bluepages"
filter = "(mail=%u)" - specify search criteria
base_filter = "(objectclass=person)" - specify base search criteria
}
authenticate { - enable authentication against LDAP
Auth-Type LDAP {
ldap
}
The parameters are set for working with IBM BluePages, an instance of an LDAP
service. Parameters may be different for other LDAP servers.
Configuring the client
Clients are configured in /etc/raddb/clients.conf. There are two ways to configure RADIUS clients. You can group the NAS by IP subnet (Listing 3) or you can list the NAS by hostname or IP address (Listing 4). When you follow the second method, shortname and nastype can be defined.
Grouping the NAS by IP subnet
client 192.168.0.0/24 {
secret = mysecret1 - the "secret" should be the same as configured on NAS
shortname = mylan - the "shortname" can be used for logging
nastype = cisco - the "nastype" is used for checkrad and is optional
}
The file /etc/raddb/user contains authentication and configuration information for each user.
Listing 5. The /etc/raddb/user file
1) Authentication type:
Auth-Type := LDAP - authenticate against LDAP
Auth-Type := Local, User-Password == "mypasswd"
- authenticate against the
- password set in /etc/raddb/user
Auth-Type := System - authenticate against the system password file
- /etc/passwd or /etc/shadow
Service type:
Service-Type = Login, - for administrative login
>Configuring the user for authorization
The following authentication server attribute value (AV) pair should be configured
for user authorization. It is returned to the NAS for an administrator login
request after authentication is accepted.
For a Cisco router, there are different privilege levels:
Level 1 is non-privileged. The prompt is router>,
the default level for login.
Level 15 is privileged. The prompt is router#, the level
after going into enable mode.
Levels 2 through 14 are not used in a default configuration.
The following command causes a user logging in from a network access server
to have immediate access to EXEC commands:
cisco-avpair ="shell:priv-lvl=15"
The following code handles the same task for a Cisco wireless access point:
AAA should be enabled on the router. Then, a list of RADIUS servers that will
provide AAA services for the NAS can be specified. The encryption key is used
to encrypt the data transfer between the NAS and the RADIUS server. It must be
identical with the one configured on FreeRADIUS.
Configuring authentication
aaa authentication login default group radius local
line vty 0 4
login authentication default
In this example, network administrators use RADIUS authentication. If a RADIUS
server is not available, use the NAS's local user database password.
aaa authorization exec default group radius if-authenticated
Allow the user to run an EXEC shell when logging into the NAS.
Configuring accounting
aaa accounting system default start-stop group radius
aaa accounting network default start-stop group radius
aaa accounting connection default start-stop group radius
aaa accounting exec default stop-only group radius
aaa accounting commands 1 default stop-only group radius
aaa accounting commands 15 default wait-start group radius
The router must be specifically configured to send accounting records to the
RADIUS server. Use the commands in Listing 9 to record accounting information
on NAS system events, network connections, outbound connections, EXEC operations,
and commands at levels 1 and 15.
That's it. Now let's look at configuring for a Cisco wireless access point.
The following configuration applies to the Cisco 1200 Series AP with Firmware 12.01T1.
As shown in the screen shot in Figure 2, you:
Input the server name or IP address and shared secret.
Select type as "Radius" and check "User Authentication."
Now that all the configurations have been completed, the FreeRADIUS server can
start logging all information sent by NAS, storing it in the /var/log/radius/radius.log
file like so:
Thu Mar 3 21:37:32 2005 : Auth: Login OK: [David] (from client
mylan port 1 cli 192.168.0.94)
Mon Mar 7 23:39:53 2005 : Auth: Login incorrect: [John] (from
client mylan port 1 cli 192.168.0.94)
Detailed accounting information is stored in the /var/log/radius/radacct directory. Listing 11 shows that David logged into router 192.168.0.1 from 192.168.0.94 between 19:40 to 19:51 on March 4, 2005. This level of detailed information will definitely be a help to administrators investigating security incidents and trying to maintain easily auditable records.
By following the simple steps outlined in this article, you can set up a Remote Authentication Dial-In User Service server that uses an external LDAP server to handle authentication, authorization, and accounting for your network security issues. This article has provided the following to help you accomplish this task:
An introduction to the RADIUS and LDAP servers and to the AAA concept.
A scenario to put the installation and implementation into context.
Instructions on installing and configuring the RADIUS server.
Details on configuring the network access server.
A sample of the detailed information that RADIUS will provide and manage.
These instructions can make quick work of the task of making sure protected data can only be accessed by authorized entities on your Linux system.
Configuring RADIUS describes the RADIUS security system, defines its operation, and identifies appropriate and inappropriate network environments for using RADIUS.
Visit OpenLDAP.org for more information on OpenLDAP.
