11X isn't actually an MOS (Military Occupation Speciality). Instead, it's an enlistment option. The Army does not offer a "guaranteed job" for any specific infantry MOS. Instead, one must enlist as an "11X." The "X" means that the specific job is not known at the time of enlistment.
Individuals who enlist under the 11X Infantry option attend Infantry OSUT (One Station Unit Training), which combines Army Basic Training and Infantry AIT (Advanced Individual Training), all in one 14-week course. During that training, recruits are allowed to list their specific infantry job preferences, but ultimate assignments are determined by the "needs of the Army." Upon graduation from OSUT, recruits are assigned to one of the following Infantry MOS's:
11B -- Infantryman
11C -- Indirect Fire Infantryman