Path MTU discovery method and system facing to IPV6

The present invention discloses a path MTU discovery method and system facing to IPV6, the method is: transmits messages from source nodes to target nodes through a plurality of intermediate transmitting nodes, and then the target nodes receives the messages and determines the path MTU and notices the source nodes, the intermediate transmitting nodes gets an outgoing interface link according to the received messages and judges length of the messages to be transmitted, and if length of the transmitted messages is larger than MTU value of the outgoing interface link, modifying content of the messages and then transmitting. The invention provided path MTU discovery method facing to IPV6, a source node can obtain path MTU by one detection if no packet is lost, which improving detection speed and reducing messages for detecting and reducing network load.