This regular expression will check for valid Internet Protocol (IP) address. Here we are going to search four decimal numbers groups, each separated by a dot. each set contains zero to three digits. Here regular expression check for two group which on concatenation generate a valid IP address. First group select from 3 alternatives which will find decimal number range from 0 to 255 ending with .(dot or period), exactly 3 repetitions and Second group select from 3 alternatives which will find decimal number range from 0 to 255.