Calling your broker is sound advice. Many outfits route your order usually through NITE as a first choice. Unless you have a direct access broker (TRACK DATA SECURITIES) as I do & then you could choose which broker or ECN you would want to use.
myTrack is a direct access broker, which means it allows you to designate which exchange, market maker, or ECN to send an order to. If you’re not comfortable with choosing, myTrack has intelligent order routing built in to get you a good execution. Many online brokerage firms don’t allow you to specify where your order goes, which can result in an execution that isn’t at the best possible price.