KLM allows carriage of pet dogs and cats in cabin and check-in. In both situations, the pet is to be kept in a kennel. 

If carried in cabin, the size of container has to be 46 (length) x 28 (width) x 24 (height) cm wherein the pet shall be able to stand up and lay down with ease. Total weight shall not be more than 8 kg. The reservation for carriage of pets in cabin shall be made at least 48 hours before scheduled departure time of flight. It shall preferably be done at the time of ticket booking or within 24 hours of ticket booking. 

If carried as check-in luggage, the kennel shall be IATA approved. Total weight of kennel and pet shall not be more than 75kg. 

A maximum of 3 pets per passenger are allowed in a KLM flight. 

Exceptions:
Snub  nosed dogs are allowed only in Cabin or in cargo, not as check-in baggage
French and English bulldogs, Boston terriers and pugs are not allowed in check-in or cargo.