I know of two format that use similar notation, Classless Inter Domain Routing (CIDR) and Variable Length Subnet Mask (VLSM). However the numbers after the /
is usually less than 32. However in this case it goes up to 120.
Here are some more output from a IP geolocation script I am using. Is this a valid format? According to the code https://github.com/maxmind/getting-started-with-mmdb/blob/57566b3adfd7e89a6510bf743be1577fcbf3a5dc/examples/03-iterate-search-tree.pl#L22 the format is ip/mask_length.
1.0.0.0/120
1.0.1.0/120
1.0.2.0/119
1.0.4.0/118
1.0.8.0/117
1.0.16.0/116
1.0.32.0/115
1.0.64.0/114
1.0.128.0/113
1.1.0.0/120
1.1.1.0/120
1.1.2.0/119
1.1.4.0/118
1.1.8.0/117
1.1.16.0/116
1.1.32.0/115
1.1.64.0/114
1.1.128.0/113
1.2.0.0/119
1.2.2.0/120