IP addresses are one of the backbones of the internet, acting as the target locations for packets of information that are sent between computers. For this reason, it is important that all IP addresses be unique. Classless Inter-Domain Routing (CIDR) creates subnet masks (netmasks) by signalling how many bits of the IP address should be reserved for the prefix. This ensures that the IP addresses within a domain will be unique while also ensuring there are not an excess number of unused IP addresses, increasing efficiency overall.