Method for determining a data transport unit parameter for the communication between two stations in a network of stations and network device adapted to act as a sending station

摘要

The invention concerns the technical field of a so-called Path MTU (Maximum Transmission Unit) Discovery process between two computing nodes over packet switched networks. On the path between two hosts (H1, H2, H3) in the network may exist various hops, e.g. routers (R1, R2), a packet needs to pass. Each link between two hops has its own MTU which may differ on each link. Some path MTU discovery algorithms are based on sending probe packets with the DF (don't fragment) bit set in the IP header. However, security devices, e.g. firewalls, often block ICMP messages, including the ICMP error messages that are needed for these path MTU discovery algorithms to work. In order to deal with connections, on which ICMP messages are blocked within the network nodes, the invention relies on acknowledgements of probe packets with MTU sizes of common network technology based MTU values sent back by the destination host. In addition, these common values increased by one byte are sent as well, to identify that the effective path MTU is a common MTU or in between of two common MTUs.