this is called CIDR — classless internet domain routing
/8 — means just the first octet must match, in our example, the range would be 1.0.0.1 to 1.255.255.254
/16 — first & second octet must match, in our example, the range would be 1.2.0.1 to 1.2.255.254
/24 — first, second & third octet must match, in our example, the range would be 1.2.3.1 to 1.2.3.254
/32 — all four octets must match — which is the same thing as leaving the IP address without any CIRD; in our example, the range would be 1.2.3.4 to 1.2.3.4