AAA and 802.1X Authentication

When it comes to securing the network, AAA and 802.1X authentication are two powerful tools we can use. Let me show you an example why you might want this for your switches:

Network users might bring their own wireless router from home and connect it to the switch so they can share wireless internet with all their colleagues. An access point like this is called a rogue access point and this is something you DON’T want to see on your network. It’s hard to detect because on the switch you’ll only see one MAC address. The router is doing NAT so you will only see one IP address, this is something you can’t prevent with port security.

One way of dealing with issues like this is to use AAA.

AAA stands for Authentication, Authorization and Accounting:

• Authentication: Verify the identity of the user, who are you?
• Authorization: What is the user allowed to do? what resources can he/she access?
• Accounting: Used for billing and auditing.

The idea behind AAA is that a user has to authenticate before getting access to the network. The fa0/1 interface on SW1 will be blocked and you are not even getting an IP address. The only thing the user is allowed to do is send his/her credentials which will be forwarded to the AAA server. If your credentials are OK the port will be unblocked and you will be granted access to the network.

802.1X is the mechanism that will block or unblock the interface. It’s called port-based control. In the picture above an unknown user plugged in a cable to the switch.

All traffic is being dropped with the exception of EAPoL (Extensible Authentication Protocol over LAN). EAP is what we use to exchange authentication information. Once the user has authenticated and everything is OK she is granted access to the network.

In the picture above you see the terminology that 802.1X uses. The user device is called the supplicant; it “supplies” authentication information. The switch is called the authenticator because it accepts the authentication information and passes it along to the authentication server. User information is stored on the authentication server.

There are two types of authentication servers:

• RADIUS
• TACACS+
  

The most common authentication server is RADIUS (Remote Authentication Dial In User Service). It’s a protocol that has been standardized by the IETF. TACACS+ (Terminal Access Controller Access-Control System) does a similar job but its Cisco proprietary.

There are many different RADIUS servers you can use, for example:

• Cisco ACS (Cisco’s RADIUS and TACACS+ server software)
• Microsoft IAS (you can install it on Windows server 2003 or 2008).
• Freeradius (very powerful and free)
• Integrated in network devices (Cisco’s Wireless LAN controller have RADIUS server software for example).

You now have an idea what the components are in a AAA 802.1X authentication setup. In the next lesson I will give you a configuration example how to implement this on a Cisco Catalyst Switch.