LDAP server problems

Well, at the school we are having many problems with user logins. The mac computers sit and wait and wait for the ldap server response for authentication. But the ldap server is getting overwhelmed by requests, so logging it causes many people to time out. When a user times out it adapts a default set of permissions ?administrative permissions? then logs into the desktop. Does anyone know how to lessen the load of the LDAP server? Every place were the ldap is connected has a gigabit connection. Any ideas would be great

Thanks
Jeremy