ldap_safe_connect

<?php
/*
If you don't want your PHP program to wait XXX seconds before giving up in a case when one of your corporate DC have failed, 
and since ldap_connect() does not have a mechanism to timeout on a user specified time, 
this is my workaround which shows excellent practical results.
*/
function serviceping($host, $port=389, $timeout=1)
{
$op = fsockopen($host, $port, $errno, $errstr, $timeout);
if (!$op) return 0; //DC is N/A
else {
fclose($op); //explicitly close open socket connection
return 1; //DC is up & running, we can safely connect with ldap_connect
}
}

// ##### STATIC DC LIST, if your DNS round robin is not setup
//$dclist = array('10.111.222.111', '10.111.222.100', '10.111.222.200');

// ##### DYNAMIC DC LIST, reverse DNS lookup sorted by round-robin result
$dclist = gethostbynamel('domain.name');

foreach ($dclist as $k => $dc) if (serviceping($dc) == true) break; else $dc = 0;
//after this loop, either there will be at least one DC which is available at present, or $dc would return bool false while the next line stops program from further execution

if (!$dc) exit("NO DOMAIN CONTROLLERS AVAILABLE AT PRESENT, PLEASE TRY AGAIN LATER!"); //user being notified

//now, ldap_connect would certainly connect succesfully to DC tested previously and no timeout will occur
$ldapconn = ldap_connect($dc) or die("DC N/A, PLEASE TRY AGAIN LATER.");
/*
Also with this approach, you get a real nice failover functionality, 
take for an example a company with a dozen of DC-a distributed along distant places, 
this way your PHP program will always have high availability if at least one DC is active at present.
*/