A method of operating a node in an information transmission network in a path discovery process for discovering a lowest cost combination of a plurality of paths from the source node to the destination node via links between pairs of nodes along the paths, different paths in the combination sharing no nodes from a predetermined set of nodes, wherein the intermediate node performs the steps of - receiving an instance of a path discovery message at the intermediate node, the received instance of the path discovery message comprising an indication of a path from a source node to the intermediate node that resulted in reception of the instance by the intermediate node; - forwarding an updated instance of the path discovery message based on the received instance via a link from the intermediate node to a next node, dependent on a result of testing at least one of a first, second and third condition, the intermediate node disabling said forwarding of the updated instance when the received instance meets at least one of said first, second and third condition, - testing the first condition comprising testing whether no further instance of the path discovery message received by the intermediate node has a value of a measure of path cost that is smaller than or equal to a value of said measure of path cost for the received instance when the further instance indicates a further path that contains only nodes from said predetermined set that occurs also in the path indicated by the received instance; - testing the second condition comprising testing whether the next node was also a node to which a preceding node along the path has a further link, and the value of said measure of path cost for the path from the preceding node to the next node via said further link is not larger than the value of measure of path cost for the path from the preceding node to the next node via the intermediate node, - testing the third condition comprising testing whether the intermediate node has a further link to the destination node and the value of the measure of path cost associated with the link to the next node is not less than the value of the measure of path cost associated with the further link to the destination node. - receiving an instance of a path discovery message at the intermediate node, the received instance of the path discovery message comprising an indication of a path from a source node to the intermediate node that resulted in reception of the instance by the intermediate node; - forwarding an updated instance of the path discovery message based on the received instance via a link from the intermediate node to a next node, dependent on a result of testing at least one of a first, second and third condition, the intermediate node disabling said forwarding of the updated instance when the received instance meets at least one of said first, second and third condition, - testing the first condition comprising testing whether no further instance of the path discovery message received by the intermediate node has a value of a measure of path cost that is smaller than or equal to a value of said measure of path cost for the received instance when the further instance indicates a further path that contains only nodes from said predetermined set that occurs also in the path indicated by the received instance; - testing the second condition comprising testing whether the next node was also a node to which a preceding node along the path has a further link, and the value of said measure of path cost for the path from the preceding node to the next node via said further link is not larger than the value of measure of path cost for the path from the preceding node to the next node via the intermediate node, - testing the third condition comprising testing whether the intermediate node has a further link to the destination node and the value of the measure of path cost associated with the link to the next node is not less than the value of the measure of path cost associated with the further link to the destination node.