An addition to trying to setup failover. After doing the ldap_connect, do the ldap_bind. If ldap_bind fails, use the command ldap_errno to get the error number. If the error number is 81, that represents the server is down. That is the only time we do a failover to our backup ldap server.
Another thing to consider is the error could be 49, then do
ldap_get_option($this->ds,LDAP_OPT_ERROR_NUMBER,$optErrorNumber);. This will return extended data and if the data code in that is 532 or 773, the bind failure will be caused by the password being expired and requiring a password update before the bind will succeed.
