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.