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.

  • 3
    Your list is nonsense. The stub you linked expects an integer (32bit number) as input and generates an IPv4 dot-quad ascii string. IPv4 addresses with a prefix length greater than 32 are invalid.
    – Ricky
    Jul 7, 2018 at 2:03
  • Thanks. My networking background is very limited. So thanks for confirming my suspension. Jul 7, 2018 at 13:15

1 Answer 1


Since the / value indicates the length of the subnet prefix and IPv4 uses 32 bits in total, that value can only be 0 through 32. /0 is especially used for the default route (=match anything) and /32 is sometimes used to indicate an end node.

I've seen non-standard and ambiguous notations like "" to indicate to - what should be - but your list doesn't make any sense.


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