It depends on the libertarian. Some believe in no government and others believe in very very little like fully abolishing agencies like the IRS but keeping it bare bones minimum for defense. For example:
http://www.cnbc.com/id/44942719
Which is dumb as shit because agencies like Commerce are constitutionally mandated.
The Department of Commerce is not mandated by the constitution, genius. In fact it didn't even exist until 1903.