A node (110) of a communication network forwards a first data packet (301) from a server (150) to a client (10). Further, the node detects a congestion affecting the first data packet (301). Further, the node (110) generates at least one second data packet (306) addressed to the server (150). The at least one second data packet (306) indicates the detected congestion and comprises verification information enabling the server (150) to verify that the indicated congestion relates to the first data packet (301).