Mechanisms are provided for determining a path maximum transmission unit of a path between a source node and a destination node of the path. These mechanisms transmit an echo request packet from the source node to the destination node along the path. The mechanisms further determine, by at least one intermediate node along the path, whether a size of the echo request packet is greater than a maximum transmission unit (MTU) of a next link of the path from the intermediate node to a next node along the path. Moreover, the mechanisms record, by the at least one intermediate node, the MTU of the next link in the echo request packet in response to the determination that the size of the echo request packet is greater than the MTU of the next link.