High Quality Content by WIKIPEDIA articles! Path MTU Discovery (PMTUD) is a standardized technique in computer networking for determining the maximum transmission unit (MTU) size on the network path between two Internet Protocol (IP) hosts, usually with the goal of avoiding IP fragmentation. PMTUD is performed by routers in Internet Protocol Version 4 (IPv4), while in IPv6 this function has been delegated to the end points of a communications session.