Ping IP doesn't work

[khalil]

Instead of executing ping/telnet you can try connecting to a known open TCP port on a device if it has one.

Code:

function pingtcp(ip, port)   local sock = require('socket').tcp()   sock:settimeout(1)   local res, err = sock:connect(ip, port)   sock:close()   return res, err end res, err = pingtcp('192.168.1.1', 80) log(res, err)

thank you 
does this work with ftp port 21?