Validating an IP Address with PHP

Written by Mark Sanborn: Jun 2, 2008

For security purposes, all user input should be validated before accepting. In this case we are going to run a regular expression to determine whether or not an IP address is valid. This function could be used on forms or web applications where you ask the user for an IP address.

Last week I wrote about Validating Telephone Numbers With PHP and Using PHP to Accept Only Numbers From User Input.

So here it is.

The Function

function valIP($string) {
    if (preg_match(
    '^(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)(?:[.](?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)){3}$^',
    $string)) { 
    echo $string;
    } else {
        echo 'Invalid IP Address';
    }
}

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