IP Address Space
Classful addresses
Until the early 1990s, IP addresses were allocated using the classful addressing system. The total length of the address was fixed, and the number of bits allocated to the network and host portions were also fixed.
Organizations could purchase three classes of IPv4 addresses.
The 3 main classes (see Subnet Mask if you don’t understand what /8 means)
- Class A is /8
- Class B is /16
- Class C is /24
There’s also class D and class E, but those are for special uses.
Classless addresses Classless or Classless Inter-Domain Routing (CIDR) addresses use variable length subnet masking (VLSM) to alter the ratio between the network and host address bits in an IP address. A subnet mask is a set of identifiers that returns the network address’s value from the IP address by turning the host address into zeroes.