AAA is a network protocol that define basically three functionality, Authentication, Authorization  and Accounting. It’s very useful for distributed systems to need authenticate users to have access for a specific services. In this post We’ll configure FreeRadius as AAA server and configure a Cisco device to allow login connections across ssh with the radius users configured on the server.

AAA-communication

The devices used in this scenario are:

– Cisco Router: 192.168.0.254/24

– Debian Server (FreeRadius): 192.168.0.1/24

Freeradius configuration

– Install freeradius:

# apt-get install freeradius

– Edit clients configuration file:

# vi /etc/freeradius/clients.conf

client 192.168.0.254 {
secret = shar3k3y
nastype = cisco
shortname = rcentral
}

– Add the new user to allow login to our router with a privilege level of 15:

# vi /etc/freeradius/users

admin Cleartext-Password := "[email protected]"
Service-Type = NAS-Prompt-User,
Cisco-AVPair = "shell:priv-lvl=15"

– Restart freeradius:

# service freeradius restart

Router configuration

– Defining new aaa login configuration:

rcentral#config term
rcentral(config)# aaa new-model
rcentral(config)#radius-server host 192.168.0.1 auth-port 1812 acct-port 1813 key shar3k3y
rcentral(config)# aaa authentication login default group radius local

With this configuration if the radius server fails, the device will use local users for the authentication.
– Configuring ssh and use radius to authenticate the users:

rcentral#config term
rcentral(config)# ip domain name mydomain
rcentral(config)# crypto key generate rsa modulus 1024
rcentral(config)# ip ssh version 2
rcentral(config)# line vty 0 15
rcentral(config)# transport input ssh
rcentral(config)# login authentication default

Configuring authorization and accounting

– Authorizing users to run an exec shell if the authentication is success:

rcentral(config)#aaa authorization exec default if-authenticated

– Configuring accounting for all system level events and exec shell sessions:

rcentral(config)#aaa accounting system default start-stop group radius
rcentral(config)#aaa accounting exec default start-stop group radius

– Check accounting start and stop events of a login user:

# cat /var/log/freeradius/radacct/192.168.0.254/detail-20130107

Mon Jan 7 14:25:07 2013
Acct-Session-Id = "0000000A"
User-Name = "admin"
Acct-Authentic = RADIUS
Acct-Status-Type = Start
NAS-Port = 2
NAS-Port-Id = "tty2"
NAS-Port-Type = Virtual
Service-Type = NAS-Prompt-User
NAS-IP-Address = 192.168.0.254
Acct-Delay-Time = 0
Acct-Unique-Session-Id = "df599de6a2047d4b"
Timestamp = 1357565107
Request-Authenticator = Verified

Mon Jan 7 14:29:05 2013
Acct-Session-Id = "0000000A"
User-Name = "admin"
Acct-Authentic = RADIUS
Acct-Terminate-Cause = User-Request
Acct-Session-Time = 239
Acct-Status-Type = Stop
NAS-Port = 2
NAS-Port-Id = "tty2"
NAS-Port-Type = Virtual
Service-Type = NAS-Prompt-User
NAS-IP-Address = 192.168.0.254
Acct-Delay-Time = 0
Acct-Unique-Session-Id = "df599de6a2047d4b"
Timestamp = 1357565345
Request-Authenticator = Verified

Sources

http://www.cisco.com/en/US/docs/ios/security/command/reference/sec_a1.html#wp1088470
http://wiki.freeradius.org/vendor/Cisco
http://www.cisco.com/en/US/products/sw/secursw/ps2086/products_user_guide_chapter09186a008007e364.html

Configuring FreeRadius for AAA Cisco clients
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