Hi Chris, thanks for the reply. In that case, would the other two be uniqueness (each IPv4 address must be unique within its network) and that every host within the same network share the same network address? Or that addresses have a hierarchical structure (4 octets, first part belong to network, second part the specific device in the network) - or is this included within the class property. Apologies, I am struggling to infer exactly 3 properties from the lecture 7 - if you have any guidance?