Netmask, CIDR and the size of networks

The following table translates the traditional netmask format to its CIDR notation. Additionally you can see how many addresses can exist in a subnet with a certain netmask.

php $headers = array(“Netmask”, “CIDR”, “Nr of IPs”); $rows = array(); $rows[] = array(“255.255.255.255”, “32”, “1”); $rows[] = array(“255.255.255.254”, “31”, “2”); $rows[] = array(“255.255.255.252”, “30”, “4”); $rows[] = array(“255.255.255.248”, “29”, “8”); $rows[] = array(“255.255.255.240”, “28”, “16”); $rows[] = array(“255.255.255.224”, “27”, “32”); $rows[] = array(“255.255.255.192”, “26”, “64”); $rows[] = array(“255.255.255.128”, “25”, “128”); $rows[] = array(“255.255.255.0”, “24”, “256”); $rows[] = array(“255.255.254.0”, “23”, “512”); $rows[] = array(“255.255.252.0”, “22”, “1.024”); $rows[] = array(“255.255.248.0”, “21”, “2.048”); $rows[] = array(“255.255.240.0”, “20”, “4.096”); $rows[] = array(“255.255.224.0”, “19”, “8.192”); $rows[] = array(“255.255.192.0”, “18”, “16.384”); $rows[] = array(“255.255.128.0”, “17”, “32.768”); $rows[] = array(“255.255.0.0”, “16”, “65.536”); $rows[] = array(“255.254.0.0”, “15”, “131.072”); $rows[] = array(“255.252.0.0”, “14”, “262.144”); $rows[] = array(“255.248.0.0”, “13”, “524.288”); $rows[] = array(“255.240.0.0”, “12”, “1.048.576”); $rows[] = array(“255.224.0.0”, “11”, “2.097.152”); $rows[] = array(“255.192.0.0”, “10”, “4.194.304”); $rows[] = array(“255.128.0.0”, “9”, “8.388.608”); $rows[] = array(“255.0.0.0”, “8”, “16.777.216”); $rows[] = array(“254.0.0.0”, “7”, “33.554.432”); $rows[] = array(“252.0.0.0”, “6”, “67.108.864”); $rows[] = array(“248.0.0.0”, “5”, “134.217.728”); $rows[] = array(“240.0.0.0”, “4”, “268.435.456”); $rows[] = array(“224.0.0.0”, “3”, “536.870.912”); $rows[] = array(“192.0.0.0”, “2”, “1.073.741.824”); $rows[] = array(“128.0.0.0”, “1”, “2.147.483.648”); $rows[] = array(“0.0.0.0”, “0”, “4.294.967.296”); print theme(“table”, array(‘header’ = $headers, ‘rows’ => $rows)); ?>