kennel cough can have different causes - viruses, bacteria and mycoplasma. the bacteria and mycoplasma respond to treatment with antibiotics, but viruses don't. but even then secondary infections might develop, possibly even pneumonia.
if a dog has a good immune system, it can usually fight it off on it's own within 2 weeks or so. but if symptoms worsen (nasal discharge, abnormal lung sounds, acting depressed etc.) you must take him in for treatment.
also, keep him isolated from other dogs until he is completely over this, kennel cough is highly contagious.