In order to free more American troops for combat duties in Afghanistan, the U.S. Army wants to hire civilian contractors to handle most of the base security duties. Unlike in Iraq, in Afghanistan U.S. troops handle base security, in addition to their other duties. But as more U.S. units, with combat experience on Iraq, arrive in Afghanistan, they note how much troop time is spent on guard duty. This means troops are less available for other things, like fighting the Taliban.
Unlike Iraq, it's possible to use more Afghans for security jobs, in addition to foreigners. It was only gradually that Iraqis were hired for more security jobs, mainly because Iraqis were easier to bribe or threaten into letting terrorists in. While that's also a problem in Afghanistan, if you use non-Pushtuns for bases in the south, you can generally rely on these Tajiks, Uzbeks and Hazaras to resist Pushtun bribes and threats. These security personnel, as in Iraq, would live on the American bases. On smaller bases, U.S. troops would still handle most security duties, and would always supervise overall security on bases.