GPO loopback processing is a mechanism that allows user policy to takes effect only on certain computers. Normally, user policy is linked to the user OU and will be applied regardless of which computer the user is signed in. However in this case, user policy is linked to the computer OU and will not takes effect to the user when signed in to computers outside this OU. The user policies applied this way can replace the normal policy or be merged with it. Administrator must know how to enable GPO loopback processing and understand which mode that suits the condition.