The present invention relates to a method for improving IP fragmentation and transmission of user payload between a User Equipment, UE (10), and a Peer Node, PN (14). The payload is transmitted through a transmission path enabled by at least a first (17,18) and a second (17,18) established tunnel, said tunnels connecting a first (11), (13) and a second (11, 13) node in a Packet Core Network, PCN. The method comprises the steps of: The first node (11,13) fragments (19) at least one received payload packet (15) into fragments (16) on the basis of a minimum Maximum Transmission Unit, MTU, for an upper IP layer of the transmission path. The first node (11,13) encapsulates (20) said fragments at the entry of the first tunnel (17, 18). What particularly characterizes the method is that it further comprises a step where the first node (11,13) determines (21) the MTU for the upper IP layer of the transmission path on the basis of an MTU of a lower IP layer of the transmission path and on the basis of the size of at least one additional tunnel header for the encapsulated fragments (16).