Network access control?

I would like to know about information about network access control

When a computer connects to a computer network, it is not permitted to access anything unless it complies with a business defined policy, including anti-virus protection level, system update level and configuration

What if the computer is being checked by a pre-installed software agent ?

it can only access resources that can remediate (resolve or update) any issues. Once the policy is met, the computer is able to access network resources and the Internet, within the policies defined within the NAC system

Can you elaborate about NAC ?

NAC is mainly used for endpoint health checks, but it is often tied to Role based Access. Access to the network will be given according to profile of the person and the results of a posture/health check.

Can you give any example ?

For example, in an enterprise, the HR department could access only HR department files if both the role and the endpoint meets anti-virus minimums.

What is the Best access control systems for my Network?

If you have a Cisco network (most other brands support this too), why not use 802.1X (port security). It will restrict what machines can access the network as step one. As for user access you may want to look into RADIUS, or TACACS. You can control access to Cisco systems with Cisco ACS.