Exactly which measures an international coalition takes to enforce a no-fly zone seems to vary quite a bit.
In Iraq, for example, coalition air forces operated under fairly restrictive RoEs, so that they were forced to play cat-and-mouse with violators and only whittle away gradually at Iraqi anti-aircraft defenses. In Libya, in contrast, the U.N.'s broad authorization of "all necessary measures" gave NATO a lot of leeway [source: Robinson].
As a result, the first step in Operation Odyssey Dawn, as the 2011 mission was dubbed in the United States, was not a patrol, but an attack. On day one, U.S. Navy ships and a British unleashed a barrage of 112 Tomahawk cruise missiles on 20 Libyan military targets, crippling Gaddafi's radar, command-and-control infrastructure, and anti-aircraft missile installations. The goal was to "shape" the battle space to reduce the risk to NATO pilots who eventually would patrol it [source: Robinson, Knickerbocker].
After high-altitude U.S. pilotless, drone surveillance aircraft were sent in to assess the first day's damage, U.S. Navy radar-jamming aircraft began flying over Libya as an added measure to neutralize what remained of Gaddafi's air defenses and to prevent his small air force of aging 1960s-vintage fighter jets from getting into the air. At the same time, aircraft from the United States and other NATO forces began to pound Libyan military targets, with the aim of further reducing his ability to attack rebels and civilians [source: Robinson, Knickerbocker].
The air crews who actually patrol Libyan airspace have a complicated job. According to an article on NATO's Web site, they spend about four hours being briefed about the latest intelligence, studying weather data and the positions of other coalition aircraft, and preparing and checking their equipment and plane before taking to the sky. Once in the air, they receive a second intelligence update from surveillance aircraft, and then cruise around the area, watching for any planes to enter the no-fly zone. If one is spotted, they determine whether it is a "hostile" aircraft, or one that has simply entered the airspace by mistake. Before taking any action against the intruder, they generally must obtain clearance from a commander on the ground [source: Booth].
If the patrols follow the same pattern as they did in Bosnia, they'll typically stay in the air for four to five hours, refueling in flight if necessary [source: Booth].