We propose a technique for building optical packet networks that does not require any buffering, signaling or header processing. Contentions are solved by means of an optical device that allows the first packet to go through while blocking others. Blocked packets are redirected back to their source nodes, thus notifying the latter about the packet status. We describe the design principles of the corresponding all-optical networks, assess their performance and power consumption, and give examples of application in the context of access networks and data centers.