A method to ascertain a network topology, wherein a request message is transmitted from a first network node to at least one second network node connected to the first network node, a second network node enters its associated node number in the network into the request message and forwards the request message to at least one third network node connected to the second network node, the request message is forwarded until all the network nodes arranged in the network and all connecting lines connecting the network nodes have been passed through, the request message is transmitted back to the first network node, and the network topology information, available in the form of the node numbers entered in the request message, is stored.