PHP Error Massage - Could not connect:?

[Ab Ha]

Could not connect: php_network_getaddresses: getaddrinfo failed: A non-recoverable error occurred during a database lookup.

i am getting this massage when i hit submit button.

i am using insert.php
<?php
$con = mysql_connect("root@localhost","portal","");

if (!$con)
{

die('Could not connect: ' . mysql_error());
}

mysql_select_db("portal", $con);

$sql="INSERT INTO users (username, password)
VALUES
('$_POST[firstname]','$_POST[lastname]','$_POST[age]')";

if (!mysql_query($sql,$con))
{
die('Error: ' . mysql_error());
}
echo "1 record added";

mysql_close($con)
?>

why that massage is showing? plx help