Nacelle for a turbofan, said nacelle having: - a fixed structure having a fixed cowl, - a mobile cowl that is able to move in translation with respect to the fixed cowl in a direction of translation parallel to a longitudinal axis X between a closed position in which it is moved close to the fixed cowl and an open position in which it is moved away from the fixed cowl towards the rear, so as to define between them an opening between a duct for a bypass flow and the exterior of the nacelle, - motive means intended to move the mobile cowl from the closed position to the open position and vice versa, - a blocking door mounted so as to be able to move in rotation about an axis of rotation on the mobile cowl between a stowed position in which it is positioned outside the duct and a deployed position in which it is moved across the duct, and - a deployment system provided so as to coordinate the movement of the blocking door from the stowed position to the deployed position with the movement of the mobile cowl from the closed position to the open position and vice versa, the nacelle being characterized in that said deployment system has: - a first rod having a first end and a second end, wherein its first end is mounted so as to be articulated on the fixed structure via a pivot connection about a first axis of articulation, - a second rod having a first end and a second end, wherein its first end is mounted so as to be articulated on the mobile cowl via a pivot connection about a second axis of articulation and wherein its second end is mounted so as to be articulated on the second end of the first rod via a pivot connection about a third axis of articulation, - a third rod having a first end and a second end, wherein its first end is mounted so as to be articulated on the second rod via a pegged ball joint connection, and wherein its second end is mounted so as to be articulated on the blocking door via a pegged ball joint connection, wherein the three rods (152, 154, 160) are disposed outside the duct. - a fixed structure having a fixed cowl, - a mobile cowl that is able to move in translation with respect to the fixed cowl in a direction of translation parallel to a longitudinal axis X between a closed position in which it is moved close to the fixed cowl and an open position in which it is moved away from the fixed cowl towards the rear, so as to define between them an opening between a duct for a bypass flow and the exterior of the nacelle, - motive means intended to move the mobile cowl from the closed position to the open position and vice versa, - a blocking door mounted so as to be able to move in rotation about an axis of rotation on the mobile cowl between a stowed position in which it is positioned outside the duct and a deployed position in which it is moved across the duct, and - a deployment system provided so as to coordinate the movement of the blocking door from the stowed position to the deployed position with the movement of the mobile cowl from the closed position to the open position and vice versa, the nacelle being characterized in that said deployment system has: - a first rod having a first end and a second end, wherein its first end is mounted so as to be articulated on the fixed structure via a pivot connection about a first axis of articulation, - a second rod having a first end and a second end, wherein its first end is mounted so as to be articulated on the mobile cowl via a pivot connection about a second axis of articulation and wherein its second end is mounted so as to be articulated on the second end of the first rod via a pivot connection about a third axis of articulation, - a third rod having a first end and a second end, wherein its first end is mounted so as to be articulated on the second rod via a pegged ball joint connection, and wherein its second end is mounted so as to be articulated on the blocking door via a pegged ball joint connection, - a first rod having a first end and a second end, wherein its first end is mounted so as to be articulated on the fixed structure via a pivot connection about a first axis of articulation, - a second rod having a first end and a second end, wherein its first end is mounted so as to be articulated on the mobile cowl via a pivot connection about a second axis of articulation and wherein its second end is mounted so as to be articulated on the second end of the first rod via a pivot connection about a third axis of articulation, - a third rod having a first end and a second end, wherein its first end is mounted so as to be articulated on the second rod via a pegged ball joint connection, and wherein its second end is mounted so as to be articulated on the blocking door via a pegged ball joint connection,