An IPv4 address block is a group of IPv4 addresses assigned to an organization or country. These blocks are assigned in different sizes, denoted by a slash (/) followed by the number of IP addresses contained in that block. For example, a “/16” block contains around 64,000 IPv4 addresses, while a “/26” block provides 64 IPv4 addresses.
The Classless Inter-Domain Routing (CIDR) notation specifies the starting number and size of a block, expressed as an IP number block followed by a slash and the decimal number of leading bits of the routing prefix. CIDR helps efficiently allocate IP addresses and reduce routing table sizes.IPv4 address blocks are assigned by organizations like ICANN, IANA, or regional Internet registries.