php cidr prefix to netmask

Question

I'm looking to convert a cidr prefix (e.g. /28) to a netmask (e.g. 255.255.255.240) and have not located a function for this, does one exist in php? If not, how would I go about doing this?

It is primitive math. Can be easily implemented in few minutes. — zerkms, Apr 19 '11 at 02:15
Btw, http://stackoverflow.com/questions/4931721/getting-list-ips-from-cidr-notation-in-php — zerkms, Apr 19 '11 at 02:16
nvm, got it: Got it! $cidr_mask = 24; $bin = ''; for($i=1;$i<=32;$i++) { $bin .= $cidr_mask >= $i ? '1' : '0'; } $netmask = bindec($bin); echo long2ip($netmask); — phpnoobipv4, Apr 19 '11 at 02:24

jonavon · Answer 1 · 2021-11-11T11:10:40.490

12

I wrote a class that contains a method that does this.

function CIDRtoMask($int) {
    return long2ip(-1 << (32 - (int)$int));
}

I posted the entire class as a gist.

edited Nov 11 '21 at 11:10

answered May 02 '11 at 12:34

jonavon

893
7
11

Wh1T3h4Ck5 · Answer 2 · 2018-04-03T12:45:03.237

Example #1:

function cidr2NetmaskAddr()

  function cidr2NetmaskAddr ($cidr) {

    $ta = substr ($cidr, strpos ($cidr, '/') + 1) * 1;
    $netmask = str_split (str_pad (str_pad ('', $ta, '1'), 32, '0'), 8);

    foreach ($netmask as &$element)
      $element = bindec ($element);

    return join ('.', $netmask);

  }

Usage

  echo cidr2NetmaskAddr ('194.234.213.0/28');

Output

255.255.255.240

Example #2:

function createNetmaskAddr()

  function createNetmaskAddr ($bitcount) {

    $netmask = str_split (str_pad (str_pad ('', $bitcount, '1'), 32, '0'), 8);

    foreach ($netmask as &$element)
      $element = bindec ($element);

    return join ('.', $netmask);

  }