The most obvious is a hacking cough that can sound as if your dog has something stuck in its throat. This can result in the production of white froth or mucus.
Other than the cough, generally healthy dogs may not be too ill; they may have a mild temperature and be a little off their food.
However, in very young/old or dogs which have an existing illness, kennel cough can be more severe and develop into pneumonia. There are also different strains of the infection which can be more severe than others.