> The better exchanges do have passwords on their FIX gateways. But the performance of a FIX login is especially important (there's often a race to start trading at the beginning of a session)

Better exchanges enable their FIX gateways long before they accept orders. They can signal their willingness to accept orders by sending everyone a message which says "we are open." Consider also that some exchanges trade products with disparate opening times. All the same applies at the close but in reverse. Better exchanges will tell you each of your orders is closed before they disconnect. Worse ones suggest you infer the same.